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    • CommentAuthorlineweight
    • CommentTimeMar 10th 2017
     
    Around three years ago, I completed a renovation within a Victorian end-of-terrace which involved retrofit of fairly substantial internal wall insulation to the original 9" brick walls.

    At the time my researches brought up some concerns about what happens to brickwork (especially absorbant, crumbly Victorian brickwork) when it's heavily insulated on the inside and therefore no longer sees any significant heat coming from inside the building that might help to dry out moisture.

    This is mainly simply about moisture that gets into the brickwork from rainfall. Obviously there's interstitial condensation to think about too but I am pretty confident I have a very robust airtight layer on the inside of the insulation.

    Some may be aware of simulations carried out by Joseph Little around 2010 that suggested that moisture buildup over time could be a worry.

    http://www.josephlittlearchitects.com/content/breaking-mould-5

    There was disagreement about whether these simulations accorded with what happens in real life. So I decided to take the opportunity to find out what happened in my walls over time.

    Part of the concern is about moisture in the brickwork reaching levels that could cause any embedded timber (joist ends etc) to rot. Therefore I placed sensors into sections of timber built into the inner side of the brickwork. One is in an existing floor joist. A couple in other bits of existing embedded (but redundant) timber. And a couple in strategically located bits of timber which I embedded myself (in these cases, I used pieces of timber taken out from walls elsewhere though).

    I've now just about got results for 3 yearly cycles. Graph below shows the WME (wood moisture equivalent) levels over time.

    (The high levels at the beginning reflect moisture that was introduced during installation - wet mortar etc.)

    Some thoughts at this point (based on my very non-expert analysis):
    - Too soon to say whether the trend for the midwinter peak is to decline or increase
    - Some of the sensors are indicating WME levels that could be a concern rot-wise
    - The sensor embedded in an actual joist end shows the least concern. But it's also not in the most weather-exposed location.

    I've also been recording temperature, RH, and AH. Happy to post more data if people are interested. I'd also be interested in any comments as to interpreting the significance of my results. I'm an architectural designer but not a building physicist.
      Screen Shot 2017-03-10 at 15.57.16.jpg
    • CommentAuthortony
    • CommentTimeMar 10th 2017
     
    Thanks for this, I am interested

    You say Victorian brickwork, has it been repointed with cement mortar?

    Are the gable walls in rooms on the inside or in the loft on the inside?

    is the scale on the chart % moisture content?

    Very happy to hear that the sensor in the joist ends is not showing a problem.

    Are those ground floor joists or first floor joists and do you have any under floor insulation or insulation on the walls in the floor void?
    • CommentAuthorlineweight
    • CommentTimeMar 10th 2017 edited
     
    Posted By: tonyThanks for this, I am interested

    You say Victorian brickwork, has it been repointed with cement mortar?

    Are the gable walls in rooms on the inside or in the loft on the inside?

    is the scale on the chart % moisture content?

    Very happy to hear that the sensor in the joist ends is not showing a problem.

    Are those ground floor joists or first floor joists and do you have any under floor insulation or insulation on the walls in the floor void?


    The brickwork has been (badly, before I moved in) repointed externally with cement mortar. Not very deeply so bits are already falling out.

    Internally I took the plaster off back to the brickwork. Where i did repairs I did it with a part lime part cement mix. Where I embedded timber I did it with fully lime mortar to try and keep as close to original as possible.

    There's a small partially vented cavity between brickwork and insulation.

    Gable walls at 1st storey and also in the storey above which is in the roof space. Sensors are installed at various heights in 1st storey. Floors below are in separate ownership. The cavity behind insulation is isolated from the flat below at their ceiling level. The insulation layer is continuous from that ceiling upwards. On the warm side of insulation I have mineral wool between joists in the floor separating me from below. The joist end is in the first floor so just above their ceiling. So not best one to use as representative but it was what was possible/easy to do at the time.

    Yes scale is %WME. As I understand it, >18% is potentially worry zone.
    •  
      CommentAuthorfostertom
    • CommentTimeMar 10th 2017
     
    Excellent to check these things for yourself.

    The annual peak doesn't look to be increasing anything like the year on year manner that Joseph showed.
    In fact looks like even tho it didn't completely get rid of the construction xs over 1st summer it nevertheless settled to a regular cycle.

    Got any links, names or clues to 'disagreement about whether these simulations accorded with what happens in real life'? Crucial question.

    Try to get yourself one of the free copies of http://www.buildingconservation.com/books/retrofit_subform.htm just out - really good, touches on this amongst other things.
    • CommentAuthorEd Davies
    • CommentTimeMar 10th 2017
     
    Nice to see some real data.

    Is 18% a problem if it's only for a few months and then it dries out again?

    The other possible issue with cold wet bricks is spalling when the wet freezes. Any signs of that? I don't know where you are but I'd guess none of these winters has been hard enough to really test that.
    • CommentAuthorlineweight
    • CommentTimeMar 10th 2017 edited
     
    Posted By: fostertomGot any links, names or clues to 'disagreement about whether these simulations accorded with what happens in real life'? Crucial question.


    It's what I recall from my general explorations at the time, but really it boils down to a lack of real world data in general. Especially when there are so many possible combinations of specific building fabric and climate all of which could give different results.

    In my case it looks like there's a kind of equilibrium year to year but I'm in south london where summers are warm and rainfall low compared to other parts of the country. I wonder how many extra mm of rain per year could break that equilibrium?

    Maybe it would be interesting to do a WUFI simulation of my example and see how well it matches my real world measurements. Not something I'm able to do at the moment though.
    • CommentAuthorlineweight
    • CommentTimeMar 10th 2017
     
    Posted By: Ed DaviesNice to see some real data.

    Is 18% a problem if it's only for a few months and then it dries out again?

    The other possible issue with cold wet bricks is spalling when the wet freezes. Any signs of that? I don't know where you are but I'd guess none of these winters has been hard enough to really test that.


    I don't know if the 18% is a problem if only intermittent.

    Where I am, it doesn't drop below zero very often. There is evidence of spalling but this was going on before I insulated and I think a result of the cement pointing.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 12th 2017
     
    Data is always good. Can you post up the raw data (there used to be a way to post up zip files).
    Have you correlated it to a local weather station?
    • CommentAuthorlineweight
    • CommentTimeMar 13th 2017
     
    Posted By: SteamyTeaData is always good. Can you post up the raw data (there used to be a way to post up zip files).
    Have you correlated it to a local weather station?


    Sure, I'll try and post up the data when i get a chance.

    No, I've not correlated with a local weather station but I expect this could be done.
    • CommentAuthorgoodevans
    • CommentTimeMar 15th 2017
     
    What was actually measured at each point - RH or RH+Temp - or some other data.

    Looking at the graph it looks like if one sensor has a peak event over a period of a day/week or so they all do.

    Therefore I would say that the data is dominated by the water content of the outside air and the temperature of the sensor - with each of the sensors being relatively warmer/colder to each other depending on how they are affected by the internal/external temperature (notice that in summer the lines converge due to the internal and external temperatures converging). I think any calculations/analysis involving vapour resistance will not match this data.

    I don't suppose you also took a measure of the outside air at the same time?
    • CommentAuthorlineweight
    • CommentTimeMar 15th 2017
     
    Measured at each point: Temp, RH, AH and WME.

    The graph posted above shows WME, not temperature.

    As I said above I'm not mainly interested in vapour coming from the inside of the building - I'm fairly confident that the way I've insulated means there will be negligible transfer of air or vapour from inside. My interest is mainly in the level of moisture in the brickwork, which is largely determined by rainfall and the speed at which it can dry out.

    There may of course also be more complicated things going on in the air void between the back of the insulation and the brickwork because this is partially connected to outside air and I'm assuming that moisture in the brickwork may be dispersing into this void.

    Unfortunately, no, I don't have a record of outside air temp, although I could obviously try and correlate with local weather data.
    • CommentAuthorgoodevans
    • CommentTimeMar 15th 2017
     
    Yes I understand your concern.

    I suspect AH and WME are derived from the direct measurements of temp and RH that the sensor made.

    What I am saying is that the bricks look like they are drying out as fast as the climate around your house allows with virtually no delay. Or, to put it another way, the moisture content of your bricks will be the same as any other house with similar temperature bricks. Other than the first few mm of brick subject to rain I think your data shows that the rest of the brick work (at sensor level) is mainly influenced by the AH of the outside air and the temperature of the brick (warmer bricks are dryer than colder bricks for a given AH (because the RH is lower)). Your data can confirm that hypothesis when matched to the climate data your house experienced.

    Another way to test this hypothesis is to graph the AH of all the sensors - I think they will correlate closely with each other (and as it happens with the AH of the outside air).

    BTW its great to see some real world data for vapour/humidity/condensation - there is so little of it about. If you can post the raw data I would love to play with it also. I would also like to perform similar measurements in my house - can you give details of your setup.
    •  
      CommentAuthorfostertom
    • CommentTimeMar 15th 2017
     
    Some great 'how to' info in excellent new Heritage Retrofit annual mag http://www.buildingconservation.com/books/retrofit_subform.htm - you may still be able to get a free copy.
    • CommentAuthorlineweight
    • CommentTimeMar 15th 2017
     
    Posted By: fostertomSome great 'how to' info in excellent new Heritage Retrofit annual maghttp://www.buildingconservation.com/books/retrofit_subform.htm" rel="nofollow" >http://www.buildingconservation.com/books/retrofit_subform.htm- you may still be able to get a free copy.


    Thanks - have requested one.
    • CommentAuthorlineweight
    • CommentTimeMar 15th 2017
     
    Posted By: goodevansIf you can post the raw data I would love to play with it also.


    I've now got the raw data downloaded in a csv file. As it's probably got my address and things in there I'd rather not put it up completely publicly but if you'd like to whisper me an email address, I'd be more than happy to send you a dropbox link and then you are very welcome to see what you can do with it, especially if you could report back with any comments you can draw from it.

    Anyone else interested (steamytea?) just drop me a message and I'll do the same.


    Posted By: goodevans I would also like to perform similar measurements in my house - can you give details of your setup.


    I have an account with this company:

    https://shop.omnisense.com/

    You buy the gateway and the sensors, which then report back to their servers, for a monthly fee. You can download the data at any point. So far it's worked well (except for some problems with the gateway unit interfering with other wireless systems in the house...whose system is to blame there - that's a long story).

    I could find very few other options for what I wanted to do. This seemed the best - or pretty much the only - bet. See my previous thread from when I was looking around:

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11966&page=1#Item_13
    • CommentAuthorgoodevans
    • CommentTimeMar 27th 2017 edited
     
    Ok, Lineweight was kind enough to let me trawl through his data and I report here all that I have found interesting.

    Part 1...

    In summary there are 6 sensors screwed into various bit of timber partially buried into a 9" single skin wall. The sensors measure air temperature, air relative humidity and (if screwed into something) wood moisture content. The sensors also report the air due point, and the air moisture content in g/kg (gpkg) both of which are derived from the RH and Temp. The wood moisture screws contact the wood from 5mm to 23mm below the surface of the wood and are approx 30mm apart.

    In addition there is a spare sensor 'indoors' that is not screwed to anything and so does not report the wood moisture content.

    I was able to acquire some historic readings from a local weather station for part of the period.

    Looking first at about a 6 weeks worth of g/kg humidity data from the end of 2015 (chosen because of the range of conditions during this period)

    https://www.dropbox.com/s/0u25l2r2og68mum/gpkg%20zoomin.png?dl=0

    Note 1) most of the lines closely follow each other including the pink line from the local weather station.
    2) The exceptions are the grey line of the indoor sensor and the purple line of the GableRearTop - Correction RearWallBottom sensor.

    Other than the RearWallBottom sensor the correlation indicates that the timbers are essentially bathed in fresh air from outside - in essence the timbers are at no more risk than say roof timbers in a well ventilated roof.

    The RearWallBottom Sensor does not follow this pattern - for a while I had assumed heat and moisture was coming from inside the dwelling - but I don't think so - Lineweight is it possible that this sensor (and only this sensor) is subject to an external air source? it seems affected even if the heating is turned off in the dwelling.

    The temperature graph for the same period is here https://www.dropbox.com/s/qtwdd2wnmlq5z48/temp%20zoomin.png?dl=0

    You can see that RearWallBottom does not behave like the other sensors and although is subject to air that is wetter than the other sensors - the air is warmer (no risk here as the RH ends up being lower and as a result the wood is both dryer and warmer than the other timbers). Hopefully Lightweight will be able to cast some light on this anomaly.

    End of part 1
    • CommentAuthorlineweight
    • CommentTimeMar 27th 2017
     
    Hi goodevans, thanks for your comments.

    This was puzzling me a bit because I couldn't really think why that sensor location would be producing substantially different results, and it wasn't something I'd noticed during my idle watching of things over the past couple of years.

    But then I plotted out the same period myself (just using the online system which logs my data) and I think the sensor locations have somehow got mixed up. The one that follows a different path is sensor number (3) and I'd expect (and know) that one to be different because it's embedded in a floor joist. The floor joist unlike any of the other timbers monitored passes through the insulation layer and into the heated area of the flat so I assume conducts heat to some extent. Also, directly underneath it is the ceiling of the flat on the floor below mine. A further complication is that at around the same level, there's a flat roof extending out from the brickwork wall (roof of my downstairs neighbour's extension) so the joist is not sitting in a straightforward external wall location.

    If the sensor numbers have somehow got jumbled in the CSV file let me know...I can tell you the proper numbers/locations.

    One source of other anomalies you might find would be leaks in the wall. I know there are a couple at the top, where there's a brick parapet with dodgy coping and a roof that's not been flashed in very well. These leaks (I was able to observe them before I insulated) mostly only happen when there's an intense period of rainfall. There might be a dribble of water that comes in for ten or twenty minutes and then stops but leaves some extra moisture on/in the inner face of the brickwork which depending on the location might affect some sensors more than others.
    • CommentAuthorgoodevans
    • CommentTimeMar 27th 2017 edited
     
    lineweight - my mistake I mistakenly re-ordederd the sensors. The unusual sensor is RearWallBottom (sensor 3). The graphs have been corrected.

    However - it is the air that is warm and not the joist - I don't think the joist would be able to heat the air up sufficiently.

    I think the warm air is either coming through from below as the following new year I looked like your heating went off a week but the sensor went warm several days before your heating came on. That appears to be significant heat loss from elsewhere (can you harvest that heat being thrown away)

    There were two leaks very early in the data set on one of the sensors - but nothing I have noticed since.
    • CommentAuthorlineweight
    • CommentTimeMar 27th 2017
     
    I would expect some heat to be getting through from the flat below.

    I would hope that not too much air from the flat below would be getting through...however, the construction at that point is quite complex and while I could reliably seal the cavity off from my own flat, it's quite possible that there are routes from below, perhaps through gaps within the shoddy old brickwork. In fact I added a little bit of extra ventilation between the cavity and the outside air not far above this point because this is something I was concerned about (it's a kitchen below).

    Yes there is heat loss from the flat below and effectively I harness it to some extent via my floorboards... the downstairs rooms in my flat are noticeably warmer when the flat below is occupied.

    This same effect doesn't seem to crop up in the temperature readings from the other sensors that are positioned fairly close to the floor level (but not in floor joists) which hopefully means that in those locations I've been more successful in preventing any air from the flat below getting into my behind-insulation cavity.
    • CommentAuthorgoodevans
    • CommentTimeMar 27th 2017
     
    It is worth pointing out that this so called moist air keeps the wood around that joist drier because although the air is moist it is also warm - the usual model of vapour being driven because of the vapour pressure does not apply here.

    The air is is unimpeded from the flat below - the heat and the moisture from the flat below mixes in some proportion with the heat and moisture of the outside air (wind direction plays a part here I think).

    As a result the wood moisture content for this joist falls between that of wood indoors and that of well ventilated external wood. The moisture content of wood indoors is typically lower that the moisture content of outside ventilated wood in the winter - this is true even in kitchens provided the kitchen concerned has reasonable ventilation most of the time.
    • CommentAuthorgoodevans
    • CommentTimeMar 27th 2017
     
    Part 2

    for the same period 2 more graphs are presented - one for the Relative Humidity of the air around the the sensors

    https://www.dropbox.com/s/t5qx6ojk9jq923l/rh%20zoomin.png?dl=0

    and the other for the moisture content of the wood

    https://www.dropbox.com/s/fi44ra4aw3nw5l5/woodmc%20zoomin.png?dl=0

    from this it is clear that the wood reacts slowly in respect to humidity change (and that the spare sensor is not screwed into any wood).

    The moisture content of the wood is partially effected by recent changes in humidity - presumably because the electrical path between the two sensors passes near the surface in part. However in part 3 I will also show that there appears to be an offset of +/- 2 percent from an expected level of humidity. This offset remain constant during winter and summer for each of the sensors.
    •  
      CommentAuthordjh
    • CommentTimeMar 27th 2017
     
    Posted By: goodevansand the other for the moisture content of the wood

    The green, orange and brown lines seem to show quite high moisture levels. Have these been checked with a separate moisture meter?

    FWIW, there's an odd one of my sensors that shows 99%! :shocked:
    • CommentAuthorlineweight
    • CommentTimeMar 27th 2017
     
    Posted By: djh
    Posted By: goodevansand the other for the moisture content of the wood

    The green, orange and brown lines seem to show quite high moisture levels. Have these been checked with a separate moisture meter?


    No...but these levels vary quite a bit over the year. See the image in my first post which shows the wood moisture levels through 3 yearly cycles. They seem to go from about 13/14% in summer up to 18/19% in winter.
    • CommentAuthorgoodevans
    • CommentTimeMar 28th 2017
     
    Part 3

    The moisture content of the wood on each sensor is presented here (blue line) together with an predicted value in red based on the relative humidity of the air at the sensor.

    https://www.dropbox.com/s/2oitwd9a9up03f8/Predicted%20MC%20vs%20Actual.png?dl=0

    The data shown is from the last 2 and half years from a point in time when the sensor readings were recorded every half hour.

    The red line is calculated in the following way... at each half hour take the current relative humidity of the air divide it by 5 and add 1% - lets call this value EMC. Take the estimated humidity of the wood from 30 minutes ago and amend it taking 6 parts in a 1000 from the EMC and 994 parts in 1000 from the previous value.

    The upshot of this is that the red line smothes the RH values, and creates the lag demonstrated by the actual wood moisture readings.

    If the RH of air changed and remained constant then the red line would progressively move towards the long term new moisture content of wood (RH/5+1). Every 2.4 days the line gets closer to its 'goal' by half the distance (after 7.2 days the line is within 7/8ths of its 'goal')

    This seems to be a reasonable fit to the data except each sensor reading appears to have a fixed offset from this estimate.

    Possible reasons are: each wood sample has different characteristics (heartwood,sapwood, density, age etc). Each piece of wood sits in a slightly different environment and the RH of the air is only on one side of the wood. the calibration the sensor may not be accurate (but the resolution is high).

    Notice however that the wood subject to the moist air from the flat below is the driest (and predicted to be the driest) of the lot.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 28th 2017
     
    I am away for a few days, so may get some time to look at the data again.
    • CommentAuthortony
    • CommentTimeMar 28th 2017
     
    Things near heat sources will always be drier, i.e. Near the flat below.

    I am concerned about moisture readings up near 20% - is there any evidence of white spots on the wood?
    • CommentAuthorlineweight
    • CommentTimeMar 28th 2017
     
    Posted By: goodevansPart 3

    The moisture content of the wood on each sensor is presented here (blue line) together with an predicted value in red based on the relative humidity of the air at the sensor.

    https://www.dropbox.com/s/2oitwd9a9up03f8/Predicted%20MC%20vs%20Actual.png?dl=0" rel="nofollow" >https://www.dropbox.com/s/2oitwd9a9up03f8/Predicted%20MC%20vs%20Actual.png?dl=0

    The data shown is from the last 2 and half years from a point in time when the sensor readings were recorded every half hour.

    The red line is calculated in the following way... at each half hour take the current relative humidity of the air divide it by 5 and add 1% - lets call this value EMC. Take the estimated humidity of the wood from 30 minutes ago and amend it taking 6 parts in a 1000 from the EMC and 994 parts in 1000 from the previous value.

    The upshot of this is that the red line smothes the RH values, and creates the lag demonstrated by the actual wood moisture readings.

    If the RH of air changed and remained constant then the red line would progressively move towards the long term new moisture content of wood (RH/5+1). Every 2.4 days the line gets closer to its 'goal' by half the distance (after 7.2 days the line is within 7/8ths of its 'goal')

    This seems to be a reasonable fit to the data except each sensor reading appears to have a fixed offset from this estimate.

    Possible reasons are: each wood sample has different characteristics (heartwood,sapwood, density, age etc). Each piece of wood sits in a slightly different environment and the RH of the air is only on one side of the wood. the calibration the sensor may not be accurate (but the resolution is high).

    Notice however that the wood subject to the moist air from the flat below is the driest (and predicted to be the driest) of the lot.


    If I understand correctly you're testing the idea that the moisture content of the wood is driven by the humidity of the air which in turn simply follows the humidity of the external air. Is that right?

    What I was anticipating was that the moisture content of the wood is mainly driven by the moisture content of the brickwork which is driven by rainfall (and any conditions which speed/slow the drying out of the brickwork). Is your feeling that the data don't match this?

    I would imagine that rainfall might raise the moisture content of the brickwork which might then raise the humidity of the air in the cavity which could then be followed by a raise in moisture content in the timber. So the timber moisture content would lag behind the air humidity but not actually be caused by it, if you see what I mean. I guess to test this we'd need to try and figure in rainfall data.

    My impression (just looking at the graphs from time to time over the past few years) is that I have seen spikes in the moisture content readings following particularly rainy periods.
    • CommentAuthorlineweight
    • CommentTimeMar 28th 2017
     
    Posted By: tonyThings near heat sources will always be drier, i.e. Near the flat below.

    I am concerned about moisture readings up near 20% - is there any evidence of white spots on the wood?


    It's not possible to see the timbers now without dismantling the internal insulation.

    I'm not directly concerned about the timbers showing readings up near 20% because none of them are doing anything structural. However, it raises a little bit of concern about other timbers which I haven't got sensors in which *are* structural - namely joist ends. The one I'm monitoring seems to be fine but it's not typical of all the other joist ends.

    Unfortunately I haven't got monitors in more joist ends just because of the timing of when they got covered up compared to when I managed to get the monitoring system sorted out. I am thinking of trying to uncover another joist end somewhere to install my "spare" monitor in it and see what's happening.
    • CommentAuthorlineweight
    • CommentTimeMar 28th 2017
     
    To hopefully help explain things a bit better here's a drawing (diagrammatic only) showing the basic arrangement of things and where the sensors are.
      Screen Shot 2017-03-28 at 10.01.44.jpg
    • CommentAuthorlineweight
    • CommentTimeMar 28th 2017
     
    One of things that you can maybe see in my diagrams is that no joist ends are in a location where they have an extent of insulated brickwork above and below. The first floor ones all have my neighbours' flat directly below, and the second floor ones are just below the eaves (where there is continuous ventilation to the external air, and where the brickwork the sit in is protected from rain to some extent by the overhang of the roof). This (I hope) means that they are all in relatively low risk locations. But it means that any monitoring I do in the joist ends themselves isn't necessarily so helpful to someone wanting to look at joist ends where they are in exposed brickwork and where the internal wall insulation continues above and below them.
   
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