Housing - Renovation: Pumped insulation to underfloor void

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- CommentAuthorMike George
- CommentTimeFeb 9th 2012
But not all of it is in the warm is it? What about joist ends and joists abutting gable walls? I've asked this question on all of these polybead threads
- CommentAuthorpmagowan
- CommentTimeFeb 9th 2012
This is the job of EWI and perimeter insulation. Look at VH's website and the work he does to avoid this cold bridge. I think, as shown by your earlier pictures, the old way fails here too. The new way could fix this problem with some effort.
- CommentAuthorMike George
- CommentTimeFeb 9th 2012
Neither Ewi or perimeter insulation will eliminate the masonry cold bridge vertically downwards. insulating the internal structure makes the ground colder and thereby increases the temperature gradient. If dew point is reached within this zone then timbers are at risk.

This scenario is even worse where the masonry is already damp. Warming up timbers in a damp environment is not a smart move. I have recently had to deal with a dry rot outbreak which resulted from warming up damp timbers.

I have seen VH's website. He has some great ideas there. This isn't one of them though.

In my view advocating any building work which is not based on established certified methods is at best irresponsible.
- CommentAuthorpmagowan
- CommentTimeFeb 9th 2012
The problem is if we stick with established methods we would still be in mud huts. EWI with perimeter insulation (leca french drain style) can only serve to heat the walls at the level where the joists end. There will be a cold bridge but it will be less than prior to insulating. In essence the heat from the house will try and go down the wall and under the EWI then out and under the leca. This is a distance of a couple of meters and so the bridge is not huge. As per VH's temperature models it should be posible to get the cold bridge down to aceptable levels in even the most extreme times of the year (how often is it minus 10C?). Your joist ends are then sitting in comparitively warm and dry conditions and can ventilate up into the house. The alternative is to leave your joists cold and wet and let a gale blow under your house to prevent rot, which also has the effect f giving you cold feet. I can not see how it is doing anything other than improving the conditions. I see your point about heating up wet timber to a temperature suitable for rot but I would like the timber to start off dry and remain so i.e. dont treat the symptoms treat the problem (poor construction).
- CommentAuthorMike George
- CommentTimeFeb 9th 2012 edited
You seem to be suggesting that all joist ends are wet, they are not. Where there is adequate ventilation, they do not get wet as a result of interstitial condensation [in the UK]. If they are wet through other reasons, like penetrating damp, then thats usually a remedial issue rather than poor design. Broken drains, cracked render etc.

Ventilating floors is good design. It is well established and proven. It is Certified. It is Best Practice. What you propose is none of these.

Back to the masonry thermal bridge. In most of the houses I've worked on [and thats 30 odd years worth] there is nowhere near a 'couple of meters' between the joists and the cold ground. Often existing houses have foundations at the shallow end of suspended floors at no more than 225mm deep. And at the shallow end they meet solid floors, often with external ground levels higher than internal floor level. There are many questions from OP's here where this is the scenario. So there is a significant thermal bridge, and you are missing the point that insulating a void makes the ground surface *colder* increasing the likelihood of the dew point being within or on the surface of the masonry. This is where timbers are often adjacent to it. And unless this is firmly investigated first, there is no guarantee that wet rot is not already present. This was the case with the job I mentioned above. Some bright spark poorly insulated a cavity leaving voids where joist ends were encased in the masonry- result dry rot.

Regarding VH's modelling, I have asked him on several threads to explain and justify how the software can model such complex heat and vapour flows accurately. He has not.
- CommentAuthorpmagowan
- CommentTimeFeb 9th 2012
The 'couple of meters' I talk about is the path the heat has to take. If you have perimeter insulation then you are warming the wall right down to the founds. So the ground on the inside will be relatively warm with a gradual drop off as you follow the 2 meter path from inside the house, under the founds to outside completely cold ground. All you need to go is warm it up enough that the dewpoint is below your joists and problem solved. Earth is a relative insulator and has lots of mass so a long thermal route would solve the dewpoint problem.

Ventilation may be the status quo but it is a rubbish idea when it comes to thermal efficiency. Efficiency is important and thus in order to make an old house better it must be improved. Obviously while you do this you must make allowances for the structure and protect it. I can not see any significant downside to warming all the timber inside the thermal envelope. If ventilated in winter the timbers must be getting -10C air flowing over them, cooling them. The warm damp air from the house must then condense on them. I live in such a house and condensation is the biggest problem. It is like the frames of single glazed windows rotting from condensation. Double glazing cures this. Warm and dry has to be the solution! Not cold, wet and ventilated.
- CommentAuthorMike George
- CommentTimeFeb 9th 2012 edited
The shortest heat flow distance is from the air next to the floor next to the wall to the base of the wall. This is typically 225mm - say 600mm on existing solid walled housing, which accounts for around 70% of UK stock. Can you explain how this is anywhere near 2m please? Unless of course you add around 1.5m of wing insultion to the exterior perimeter.

And are you seriously suggesting this is an economically viable proposition to solve heat loss in a suspended wooden floor? Fill the floor with beads; externally insulate the perimeter, and add wing insulation? Far simpler, cheaper and better to replace it with a ground bearing slab.

Doing this with even a modest amount of insulation will reduce more than 70% of the heat lost through a floor. A u-value of around 0.35W/m2K is the economic optimum, and any money spent achieving lower than this is better spent elsewhere. Selling the reclaimed joists and floorboards will even part fund the work
- CommentAuthorfostertom
- CommentTimeFeb 10th 2012
Related discussion in http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=8594&page=1#Item_1
- CommentAuthorViking House
- CommentTimeFeb 10th 2012 edited
We pumped the existing floor of this house with beads and built a Passive Extension to the rear in 2009. I drop in from time to time when passing and test the air quality and the energy bills etc, there's a floorboard beside the front wall that's easily removed, the moisture level in the joist in the wall has been a steady 12% with the last year which is similar to the moisture level of a joist in the middle of the house.
My conclusions;
The joist isn't getting any wetter even though its exposed to a damper than outside environment.
The amount of moisture that moves through materials by vapor diffusion is insignificant.
Stop the leaks and don't worry about vapor diffusion which seems to move through materials at a slower rate than the materials ability to dry out!
There has never been a documented case of decay in a buildings structure as a result of moisture moving through materials by diffusion.
- Paul Whelan Front.jpg
- Paul Whelan Rear.jpg
- CommentAuthorViking House
- CommentTimeFeb 10th 2012
This document may be useful to the discussion http://viking-house.co.uk/images/web-pages/Downloads/Moisture%20Buffering%20Effect%20of%20Wood%20Products.pdf
- CommentAuthorfostertom
- CommentTimeFeb 10th 2012
Posted By: Viking Housenever been a documented case of decay in a buildings structure as a result of moisture moving through materials by diffusion
unless liquid moisture content of the (timber) material reaches the 18% (is that right?) rot trigger point, by condensation as a result of its temp as the moisture vapour supply diffuses thro it?
- CommentAuthortony
- CommentTimeFeb 10th 2012
Thoughts from my friend in Iceland, he says:-

Any risk would be hugely reduced in older buildings if they were consrtucted using lime mortar and have not foolishly been cement renrered or pointed.

Here in Iceland we love the ideas and thoughts of all Vikings, may many follow your practices.

Up here we dont bother with insulation, the only reason we use double glazing is that we cant buy single-glazed window frames any longer. (dg is less sustainable as it often fails in our extreme climate and has to be reÃ°laced)

Our domestic energy source is clean and non nuclear being geothermal with a little hydro.
- CommentAuthorMike George
- CommentTimeFeb 10th 2012 edited
Posted By: Viking HouseWe pumped the existing floor of this house with beads and built a Passive Extension to the rear in 2009. I drop in from time to time when passing and test the air quality and the energy bills etc, there's a floorboard beside the front wall that's easily removed, the moisture level in the joist in the wall has been a steady 12% with the last year which is similar to the moisture level of a joist in the middle of the house.
>

How do you know the moisture content in a joist end? Or anywhere else under the floor such as where wall plates sit on intermediate stub walls? Or in any void which may be amongst your poly beads?
Posted By: Viking House My conclusions;
The joist isn't getting any wetter even though its exposed to a damper than outside environment.
>

I donâ€™t follow, how is the environment damper than outside?
Posted By: Viking House
The amount of moisture that moves through materials by vapor diffusion is insignificant.
>

You conclude this from observing the top edge of a joist adjoining a warm environment do you? Can you point me to something in a text book or peer reviewed paper which backs up your conclusion please? Is there something specific in the document you linked to?
Posted By: Viking House
Stop the leaks and don't worry about vapor diffusion which seems to move through materials at a slower rate than the materials ability to dry out!
There has never been a documented case of decay in a buildings structure as a result of moisture moving through materials by diffusion >

You mean not one that youâ€™ve read I presume? Or are you saying that vapour diffusion cannot result in timber or other material degradation?
What about my observations here? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=7526&page=3
I wonâ€™t post all of the pictures from that thread but isnâ€™t the evidence shown in this picture that condensation does at the very least contribute to timber degredation? Furthermore isn't it the case that vapour diffusion and water ingress can be interdependent? The picture shows evidence of condensation on the underside of carpet insulation.
- CommentAuthorMike George
- CommentTimeFeb 10th 2012 edited
Working link to the picture above

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=7526&page=3

And a picture of the timber degredation for context
- CommentAuthorMike George
- CommentTimeFeb 10th 2012
Posted By: tonyThoughts from my friend in Iceland, he says:-

Any risk would be hugely reduced in older buildings if they were consrtucted using lime mortar and have not foolishly been cement renrered or pointed.

Not many of them around in the UK though are there
- CommentAuthortony
- CommentTimeFeb 10th 2012
Sadly mainly due the insistance of lenders far too many have been wrecked by the inapprocriate use of cenent.
- CommentAuthorMike George
- CommentTimeFeb 10th 2012
Very true
- CommentAuthorViking House
- CommentTimeFeb 10th 2012 edited
Hi Mick, The joists in your pictures were, as you said yourself, damaged by moist air condensing on the joists, this is condensation from damp air that leaked into the floor void, not diffusion. I never claimed that condensation doesn't occur on joists.
In my case there's no air movement beneath the floor because the vents are closed, lack of bulk air movement means lack of moisture present to condense, and the joists are anyway too warm for condensation. The joists become similar to an unpainted kitchen table or a worktop, you never get condensation on these items.
I pulled the beads away from around the joist where it enters the wall, stuck the humidity monitor into the joist end beside the wall and got a 12% humidity reading. I don't need somebody to do a 3 years peer reviewed Thesis on it, I just opened the floor and checked it and its fine!
We generate moisture from showers, cooking, drying clothes and through respiration so the interior moisture levels are usually higher in winter when the condensation risk is highest.
The document I linked to shows how slow moisture diffuses through materials, I'm talking about moisture movement through the floorboards, then the joists, which is the only way moisture can get down beneath the floor now because the usual method (leakage) has been closed off.
- CommentAuthorMike George
- CommentTimeFeb 10th 2012 edited
You are twisting my words. I didn't say the joists were damaged by moist air condensing on the joists, though it is was probably a contributing factor, excaserbated by cold wet masonry with insufficient height above the external ground level. Also insufficient through ventilation. I certainly didn't say it was diffusion. I said that the risk of interstitial condensation can be heightened by diffusion of vapour through or around a filled void where a dew point exists. I said that sub-floor condensation is mitigated by adequate ventilation, and I said that wet rot is the worst case scenario where such ventilation exists.

You need to read the thread I linked to get the full context of this. I notice you didn't follow through with the debate we were having on this subject there. You sidestepped my questions, the same as you are doing here.

Ignoring the ones you skipped over on my last post, I'll ask you some of the more important ones again.

How do you know what effect filling a void with poly beads will have on timber wall plates sat directly on intermediate stub walls?

How do you know that some of the timbers you have warmed have no wet rot in them prior to your upgrade?

And how does the software you use model such complex vapour movement through the edge conditions such as joist ends, joists alongside masonry and wall plates on stub walls?
- CommentAuthorViking House
- CommentTimeFeb 11th 2012 edited
Posted By: Mike GeorgeYou are twisting my words. I didn't say the joists were damaged by moist air condensing on the joists, though it is was probably a contributing factor, excaserbated by cold wet masonry with insufficient height above the external ground level. Also insufficient through ventilation. I certainly didn't say it was diffusion. I said that the risk of interstitial condensation can be heightened by diffusion of vapour through or around a filled void where a dew point exists. I said that sub-floor condensation is mitigated by adequate ventilation, and I said that wet rot is the worst case scenario where such ventilation exists.
I was talking about diffusion in this thread and you posted photos of rotten joists with no proof that they rotted by diffusion. If you cut off the air supply then there's no moisture present at the Dew Point to condense. Ventilating beneath floorboards can also bring in a lot of moist air. The science article you linked to shows the benefit of insulating beneath the joists like we do.

Posted By: Mike GeorgeHow do you know what effect filling a void with poly beads will have on timber wall plates sat directly on intermediate stub walls?
My own house has EPS beads pumped beneath the timber floor, I have a thermocouple beneath the beads and its showing a constant temperature of 14 degrees throughout summer and winter, stub walls are usually in the middle of the house where its warmer, so there's no risk there!

Posted By: Mike George How do you know that some of the timbers you have warmed have no wet rot in them prior to your upgrade?
When we lift 1 or 2 floorboard to pump the EPS beads, the EPS guys have one of those flashlight cameras with a flexible head that they use to check walls before they pump in EPS beads, so we usually have a good look around first. These houses are usually 60 years+ so and problems with rotten joists will have raised their head before now.

Posted By: Mike George And how does the software you use model such complex vapour movement through the edge conditions such as joist ends, joists alongside masonry and wall plates on stub walls?
Therm shows the temperature of the cold bridges and the amount of heat-loss and WUFI shows that when you externally insulate walls they get dryer every year for the 5 years of the simulation.
I never claimed to be using software that modeled vapor movement through materials.

Posted By: Mike GeorgeBut not all of it is in the warm is it? What about joist ends and joists abutting gable walls? I've asked this question on all of these polybead threads.
I tested the top and the bottom of the joist end where it meets the external wall in the above house and it shows a 12% moisture level, which is pretty dry so no problem there! I didn't expect the joist ends to be damp because they don't reach Dew Point and there's little moisture present to condense because of the high airtightness levels .
- CommentAuthorMike George
- CommentTimeFeb 11th 2012 edited
You're still twisting things. For example, you claim the article I linked to justifies your filling of voids with polybeads in Ireland - it does not - and you know it. For a start it relates to the US climate, where vapor movement can be the opposite direction of that experienced in the UK [and Ireland?]

Your position is based on observation of a few properties where so far no problems have come to light. I can agree that in some properties there may never be problems, and you will indeed benefit those properties.

But you cannot apply such a limited sample of observations to housing throughout the UK.

My position is based on building methodolgy developed, tried and tested for hundreds of years.

In more recent times this has been backed up by:

Manufacturers Specification and Certification of appropriate products and installation procedures [remedial insulation for example]; this based on the above empirical evidence and also laboratory tested evidence. These instruments are the requirements of UK Building Regulations

In the UK you would not get away with the method you are undertaking and you would receive instruction from Building Control for the removal of the beads

You could also be sued for damages where any of your actions result in necessary remedial works.

It is possible that even recommending works here which knowingly contravene UK building regulations could be viewed as litigatuious should their implementation result in damage to property. Knowingly carrying out such work here is certainly an offence.

So anyone thinking of doing this beware

I've had my say on this thread for now
- CommentAuthorborpin
- CommentTimeFeb 11th 2012
Posted By: Mike GeorgeYour position is based on observation of a few properties where so far no problems have come to light. I can agree that in some properties there may never be problems, and you will indeed benefit those properties.
Pretty good way to start I suggest.

Posted By: Mike GeorgeMy position is based on building methodolgy developed, tried and tested for hundreds of years.
And that methodology has never had any problems (well apart from rotting timbers, condensation, wasted heat...). Oh and I suggest hundereds of years since advice from building control has changed is stretching things (though it does seem like they are in the dark ages).
- CommentAuthorViking House
- CommentTimeFeb 11th 2012 edited
The building science article Mike linked to http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces is dealing with condensation on cold joists just like we are. The moist air in the article is coming from outside in summertime, in our case its coming from the leaky house above in wintertime and we also have cold joists, so there are similarities, moist air - cold joists. The conditioned crawl space (pic 5) bears similarity to pumping EPS beads beneath the floor because the joists are too warm for condensation and the vents are closed up restricting air-flow. The article states "just by warming the wood you lower itâ€™s equilibrium moisture content". The guy who wrote the article doesn't seem worried about the cold bridge (pic 5) where the joists go through the insulation (like you are) because the airflow to the joists is probably sealed like the polythene on the floor.

Beneath Figure 5 it states: "Warming the Woodâ€”Wrapping the floor framing in foam insulation lowers the equilibrium moisture content of the wood. Warm wood is dry wood. Warm wood is happy wood. One not so minor issue, changing the temperature only gets you so farâ€”the vapor drive upwards still needs to be addressed".
This also bears similarity to pumping EPS beads beneath the floor because the joists are too warm for condensation and the vents are closed up restricting air-flow. But we don't have the upward vapor drive issue because the vents are sealed!
In Sweden they ventilate cellars mostly in the Spring and Autumn or only after the 3rd day of sun in Summer when the air has dried out a bit!

Thanks Mike for your debate on this, it's needed to tease out the problems!
- CommentAuthorMike George
- CommentTimeFeb 12th 2012 edited
Oh dear, that hasn't lasted long, I find I cannot resist
Posted By: borpin
Posted By: Mike GeorgeYour position is based on observation of a few properties where so far no problems have come to light. I can agree that in some properties there may never be problems, and you will indeed benefit those properties.
Pretty good way to start I suggest.

Yes, observation is a great way to start, but much more is required.
I could draw a parallel with multifoil, where much of the manufacturers justification for their product is based on anecdotal evidence â€˜that it worksâ€™ They went through years and years attempting to gain certification by methods unaccepted by the mainstream. The only way they have managed to get their product in use is to follow the procedures for Certification set out in UK and EU law.
Do you accept their protestations the product works in a way not borne out by the established physics? Would you use multifoil to insulate a suspended wooden floor? Would you know how to? Are there any risks? How would you know what to do without manufacturers specification backed up by a BBA Certificate for example?
No, observation is nowhere near enough.
Posted By: borpin
Posted By: Mike GeorgeMy position is based on building methodolgy developed, tried and tested for hundreds of years.
And that methodology has never had any problems (well apart from rotting timbers, condensation, wasted heat...). Oh and I suggest hundereds of years since advice from building control has changed is stretching things (though it does seem like they are in the dark ages

A laughable distortion of the facts. Rotting timbers and condensation only occur in floors where the established Best Practice is NOT followed. Paramount among requirements is adequate ventilation of the void.
Yes there is wasted heat but there are many established methods to insulate suspended floors. Why would you try a risky one like filling the void?

Finally I donâ€™t know where you got this sentence from.
Posted By: borpin Oh and I suggest hundereds of years since advice from building control has changed is stretching things (though it does seem like they are in the dark ages

What I actually wrote was
Posted By: Mike George
My position is based on building methodolgy developed, tried and tested for hundreds of years.
In more recent times this has been backed up by:
Manufacturers Specification and Certification of appropriate products and installation procedures [remedial insulation for example]; this based on the above empirical evidence and also laboratory tested evidence. These instruments are the requirements of UK Building Regulations

Not quite the same is it - why are you twisting my words? Is it a straw man tactic?
- CommentAuthorborpin
- CommentTimeFeb 12th 2012 edited
Posted By: Mike GeorgeFinally I donâ€™t know where you got this sentence from.
Posted By: borpinOh and I suggest hundereds of years since advice from building control has changed is stretching things (though it does seem like they are in the dark ages

What I actually wrote was
Posted By: Mike George
My position is based on building methodolgy developed, tried and tested for hundreds of years.
In more recent times this has been backed up by:
Manufacturers Specification and Certification of appropriate products and installation procedures [remedial insulation for example]; this based on the above empirical evidence and also laboratory tested evidence. These instruments are the requirements of UK Building Regulations

Not quite the same is it - why are you twisting my words? Is it a straw man tactic?
Yes and I quoted you; You said 'hundereds of years' and it seems to me much has changed in 'hundereds of years' and some of the official techniques employed in that time have be found wanting. So just because they are approved does not make them right or perfect. If they were you would not find rotting joist in existing houses!!!
- CommentAuthorMike George
- CommentTimeFeb 12th 2012 edited
http://en.wikipedia.org/wiki/Straw_man
- CommentAuthorfostertom
- CommentTimeMar 14th 2012
Thanks to everyone - the fruits are here:
http://uploading.com/files/ad26df12/285Ja-ufloor.pdf.
Building Inspector is keen to support it, wanted the 'argument' submitted - this is it. Hope he approves, as an02ew of this forum and I have just started building it!
- CommentAuthorCav8andrew
- CommentTimeMar 14th 2012
Tom. I don't fully understand the properties of LECA, is it so free draining that the timbers carry no risk of being damp or is some form of treatment an absolute requirement. Also what scale of build do you think this method (Diag. 3) could be applied. 2 story house build, for instance ? Apologies if all these questions have been already answered in related posts.
- CommentAuthorViking House
- CommentTimeMar 14th 2012
Warm wood is happy wood!
- CommentAuthorfostertom
- CommentTimeMar 15th 2012
Cav8andrew, at this stage of the game I'd do belt n braces and have treated timber - ultimately wd be gd to lose that, as we now do with 'dry' above-ground timber.

Scale of build - entirely a struct eng question. Internal columns supporting similar upper floor main beams supporting cantilevering joists, ditto purlins supporting roof? Cd help spread the loads so not all rests on the cantilever ends of the Grd Fl joists.

As I just said in http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=8594&page=2#Item_7 ,
'the ground beams ... have v variable inset (therefore joist cantilever), due to bridging round some incredible u/ground features we're discovering! - this is a v flexible system that can be re-laid-out instantly'
The ground beams themselves can also cantilever at end. The pads can be dotted around wherever u/ground drains etc leave space. On this job we're 'building over' a pr of foul and surface water drains that have just been adopted by Wessex Water who are applying draconian standards far exceeding what the Bldg Insp wd have required hithereto.

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Housing - Renovation: Pumped insulation to underfloor void