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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

I am away for a few days, so may get some time to look at the data again.

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.

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.