Posted By: lineweightUnfortunately 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.

As I understand it, for timber moisture readings, all you need to do is bang a couple of nails into the wood, connect some bell wire to them and bring the wire to a place where you can later connect a moisture meter. I expect you have to get the nails some specific distance apart (the same as the ones on the moisture meter, presumably?) and possibly you have to think about materials to avoid galvanic couples?

So if anybody exposes joist ends, it seems to me to be worthwhile to stick the nails and wire in just in case you want to test the moisture at some later time.

I hate those prong things, I drill a hole, catch the dust, weigh it, dry it in a warm oven, re weigh, calculate the % moisture content

I don't do as much damage as the injected dpc boys do

SWAG - had to look that up - that sums it up pretty close. Divide by more than 5 and the seasonal peaks are not big enough, less than 2.4 day half life and the short term peak range isn't big enough (BTW half life = 0.5 = .994^(2.4*24*2). There is nothing I can do with the offset no matter what I did. However dividing by 5 does seem to be a fairly common rule of thumb.

In reality I suspect that the half life nearer the surface is going to be much shorter (maybe zero), at deeper levels much longer. At the surface as soon as the relative humidity reaches near 100% the wood moisture will be at around 20%. This will happen when it's foggy / raining. But it's not permanent - sooner or later the outside RH drops and the wood surface dries out.

All well ventilated rafters/battens in cold roofs will be affected in this way - but providing there is no leakage there should not normally a problem - However I have not been able to find out how much or how long or how often wood can sustain a RH events of more than 90% and not deteriorate for say 100 years.

given how closely the red line follows the blue line I think it is unlikely the offset is cause by the environment the wood is sitting in. We may never find out as the wood is inaccessible. My feeling is that the offset is more to do with the electrical characteristics of the wood - however there is a chance that the the offset is caused by each piece of wood suffering wetting/dampening due to rain on the brick side of the wood which could create a very slow response on the sensor side of the wood (but as a betting man I don't think the data indicates this).

Sorry for the late reply, I've been away for the weekend.

Yes - I could not have put it better myself. I see no evidence for rain driven dampness in the wood.

It is possible that rain driven dampness on the far side of the wood is causing the different offsets in the moisture levels at each of the different sensors - however for that to be the case - rain driven dampness would have to have to effect the wood moisture content really slowly - i.e. a series of rain events/season would have to take a couple of months or so to affect the sensors - any faster than that and the red line would not follow the blue line.

I suspect that the brickwork moisture content is also RH driven - any wetness from rain is short term, shallow and when the rain stops the outer surface of the bricks dry to the moisture content dictated by the RH.

I've been pondering for a few days.

First, rain driven dampness would cause the wood next to the brick to be wetter than the moisture than a high air RH would deliver - but any wetting at the far side of the wood would take it's time to reach the sensor.

And I would have to agree that the formula I used has been created to fit the data - not a good way to go (however dividing the RH by 5 is a common estimation of equilibrium wood moisture content).

Filling the cavity may still have potential issues however - at present the cavity air is dominated by the outside air. If this air is prevented from circulating in this region there is a chance that the moisture content could be dominated by your internal environment (which in winter is approximately 2 gpkg wetter). In addition this cavity always allows the internal surface of the bricks to be able to dry to air copiously sourced from the outside (and it is these bricks your joists are supported by - you need these bricks to be as dry as possible).

However we are getting into real areas of uncertainty here. Some of the wood does already indicate quite high levels of moisture content, I am no expert - I just like unravelling real data sets to get to nuggets of information.

Ideally some of the other regulars here should give an opinion - (insulate on the outside of the wall - no-brainer) on the inside - not so sure.

sorry I can't be more positive.

Humidity and rainfall are different and so are relative humidity and humidity, tremperature has a big influence.

I would insulate outside of wooden members, (this makes me worry about sips)

But I do agree that not all exposed wood will last that long.

At the moment the existing sensors are bathed in outside air - I see no affect on the wood or the RH sensors of any effect of rain - it may take very damp walls to show any anomalies with all that fresh air around the sensors.

Perhaps a sensor attached to the inside of the wall and a 1 meter square polythene barrier over the sensor sealed air/moisture tight at the edges against the wall. Compare that sensor with one of the others (except sensor 3) - any lumps and bumps in this new sensor not correlated to the standard sensor(s) would indicate a non-airborne water source (i.e. rain) permeating through some part of that 1m2 brickwork. If you get lumps and bumps attempt to correlate with local weather reports - (rain, direction, wind, sun etc from the Weather underground site to confirm - at least 2 stations report within a mile or so of you.)

The 1m2 barrier would emulate a worst case scenario of filling the cavity - any lumps and bumps would be bad news - it would mean your joist ends would be damper than they are at the moment. My gut feeling - its a risk - ventilation limits the detrimental effects of small leaks.

Posted By: fostertomMeteonorm is primarily for agricultural purpose, which apparently doesn't need driving rain info. I'd love to know how others manage to reliably approximate around that lack, in WUFI.

I'd have thought that any design needs to cope with a 'moderate' amount of driving rain from any direction. Where 'moderate' means that the rainscreen can resist the onslaught at the time and dry itself out to resist the next onslaught before it happens.

I would expect that in locations where there is more than moderate driving rain, there is local knowledge and custom that is best observed. But a balanced rainscreen in front of a double drainage plane will cope with almost all conditions, I believe.

Posted By: lineweightI have been wondering what the wettest part of the UK that has a tradition of brick built architecture is.

Brick is modern. Traditional architecture is stone, in those parts of the country that have stone and especially where there is exposure.

Posted By: fostertomand direction

There is speed and Velocity.
One is scalar and the other is a vector, learn the difference.

The traditional solution is to build the building, then observe which if any walls get wet enough to cause a problem and then add a rainscreen to such walls. It's only the modern vanity of the planners' aesthetic that requires prediction.

Posted By: djhBrick is modern. Traditional architecture is stone, in those parts of the country that have stone and especially where there is exposure.

Posted By: djhThe traditional solution is to build the building, then observe which if any walls get wet enough to cause a problem and then add a rainscreen to such walls. It's only the modern vanity of the planners' aesthetic that requires prediction.

I don't think I understand what point you're making. Brick is not just a modern thing; there are many areas of the UK which have used brick for many centuries. Indeed the more exposed parts of the UK tend to use stone and yes I expect this is to do with it being a more weather resistant material but it's also the case that much of the UK's west coast is to some extent mountainous and using stone is a result of the local geology as well as climate.

The reason I wondered which of the UK's traditionally-brick areas is the wettest is that there might be building methods particular to those areas which might give some clues as to whether brickwork becoming saturated through driven rain is a real and likely thing. If, for example they use a noticeably less porous brick then that suggests that it's something that's been recognised as a problem historically, and therefore something that we should be worrying about when we make changes such as adding internal insulation. If on the other hand there are areas of the UK which have a lot of rain but also have historically used brick that is similar to that common in drier areas - then maybe it's not such a worry, and it's the nature of brickwork that only the outermost part gets saturated, and other things being equal, timber embedded into its inner portion is fairly safe.

I can't think of many/any traditional UK building methods that use a rainscreen - let alone one added post-hoc - what are you thinking of?

'I can't think of many/any traditional UK building methods that use a rainscreen - let alone one added post-hoc'

Lime wash has been used as a protective layer and can act as a rain screen, often applied every autumn.