Insulating a house on stilts? Ideas?

[ABCwarrior]

Jeez- please bear with me on this....Last winter was the first in our new house, supposedly "eco" this and that- it's timber kit, larch clad, super insulated (well, from floor level up).
When the temperature dropped to below -15 we lost the water supply to the downstairs, thankfully still got all the upstairs supply(toilet/bath/sink). This happened on loads of occasions as it hit -25 (we're in the Cairngorms), and we had a few burst pipes(those braided connections popping).
The house is on stilts and sits some 30cm above the ground, the floor sections were made off site and essentially are boxes with 9mm ply attatched from below so the floor insulation sits within the floor cavity. What we found out was that all the services enter/exit the house through a large plastic conduit/pipe and when we lifted the floor adjacent to this the dust that was lying on the insulation blew up into my face- the air was being drawn in at a high rate by the multifuel stove we have so the pipes were getting supercooled. The builder and architect realise it's a combination of sh*t design and poor workmanship not sealing off the interface of the pipe to the house, so they have excavated under the house to let a joiner in to insulate it with kingspan and box it all off, which has been done well enough but doesn't fill me with any confidence because the rest of the underside of the floor has the same poorly fitted ply with gaps on the edges etc. I'm concerned that although they have sealed up the bit immediately below the problem area, that when winter comes again and the fire is roaring, air will be drawn in from further afield through these gaps, then through any holes put in joists to get the central heating pipes in?!
We have a "vent" on the floor next to the fire, but having looked under the house it doesn't connect to the outside directly so that will be getting blocked off. I'd rather leave a small window open slightly than have this vent pulling cold air through the floor space.
I'm even considering buying enough 12mm WBP to cut into lengths and screw to the base of the house all the way round, silicone sealed at the joints and with a couple of air vents in it which can be shut when the temperature really drops. I can scrape back the gravel below then back fill it to the ply once attatched to seal it from the wind.
The second phase of this housing "project" is going ahead and, surprise surprise the things are going on solid founds because it "improves thermal mass" according to the acid head architect- is that double speak for "it's warmer than a hollow friggin wind tunnel floor"!!!??

Can anyone else suggest any ideas to this?

 

[mointainwalker]

Having read through it ,I can't see what your main concern is.

Is it :

a) Making sure your pipes don't freeze or
b) Improving house insulation ?

If it's a) fit trace-heating to pipes and if it's b) you have the right ideas and need to seek out your major air-leaks.

I hope you are going after the developers for costs because I imagine that as well as conforming to thermal insulation regs on plan, they also have to build and deliver to them.

If it's a new-build, will it have had the air-tightness test ? Don't know if that was incorporated into latest regs, but should have shown up the problem you are experiencing.

 

[Nige F]

eco log burning fire whatever , it`s drawing it`s combustion air from it`s surroundings - Not through a purpose made duct that goes to outside . 1x O level tells me that isn`t a good idea . how many degrees do the architects etc. have between them

 

[alittlerespect]

Hi

Log burning stoves can emit noxious fumes which can be fatal, and the reason for the vents being open is to ensure that people cannot use such heating equipment without have a supply of fresh air. However, it sounds as if your Architect has been a touch over zealous in his design as there should be no need for a force 10 gale to be blowing through the vent.

At your risk, you could replace the existing vent with fit a 'hit and miss' air vent, but you would need to ensure that this is in an open position when you use the stove, especially when you get your draughts sorted out! As a solution, you could try a 'hit and miss' air vent and adjust the hit and miss vent, so that you get some trickle ventilation, which should be adjusted such that you would not notice any appreciable draft. And then make some sort of mechanical fixing so that the vent can never be closed any further than this position.

The real issue is that the 1 time that someone forgets to open the vent it is usually means it is their last! You may have a roaring fire going and be feeling all cosy and warm, getting a bit drowsy and put it down to being warm and comfortable, and maybe a bit tired from working (whatever) next thing you are falling asleep never to wake up again!!

Regretfully, this affect of wood burning stoves is very seldom advertised, and only generally gets into the press after a fatality, but it is known as a foreseeable risk and you should have been advised accordingly by your Architect.

The overall design of the house sounds a bit naff for such an exposed location and I was wondering if you might have some electronic copies of the drawings that you could forward, as I would be interested in commenting on the overall design of the house. I would also be interested in knowing what temperature differential the Architect used when calculating the heat losses for the building, as this would determine the insulation requirements for the whole building.

Obviously, the quality standards were not being monitored when your house was being built, and it should be between the Architect and Builder to resolve the issues with the draughts at no cost to yourself.

Final comment: thermal mass is to do with the abilty of construction materials to store energy, has been about for quite some time. Basically some building material store a certain amount of heat, and when the temperture in the room goes below that of the construction element the construction element re-emits this low level energy, but it is not as effective as some people may lead you to believe.

Regards

 

[mointainwalker]

I think the last poster is considerably exagerating the risks of wood-burning.

My own experience is that if there is insufficient air the fire will burn badly and may smoke but this should l be contained within the fire/chimney.

Personally I have never read of a fatality caused by wood-burners as the flame is enclosed and vented unlike gas-fires.

Any link to such cases alr ?

 

[alittlerespect]

Dear mountainwalker

There was a recent case where a person was asphyxiated due to the fumes given off by a wood burning stove. I suspect that the problem was related to a lack of ventilation and that there was so much draft proofing that a negative pressure was created and rather than the fumes being drawn up and exhausted out of the flue as would be expected in the normal run of things, the negative pressure sucked the fumes back into the room, much in the same as gas fires discharge CO into a room when there is an insufficient supply of fresh air. I don't know the exact case details and anyone interested in further reading would need to do their own internet search.

The likelihood of these events happening are low, but they do happen and when they do happen the results are nearly always catastrophic. If you carried out a risk assessment you would find that the severity of not providing ventilation would be severe, forget the low likelihood it does happen, so the likelihood would have to be medium at least, which would give a high risk level and safety measures would need to be introduced to ensure that such risks were mitigated, hence the requirement for the fixed ventilation.

Regards

 

[alittlerespect]

Getting back to ABCwarrior

Rather than fix ply to the underside, which has a rather limiting U value, you should consider sticking a mimium 50mm or ideally 100mm thickness of PIR insulation to the underside of the floor, in saying this I do realise that you have limited space and a way out of this may be to dig a series of shallow trenches which the installer could then slide along. I would have thought a trench every 4ft (120cm in new currency!)
Just as a note I would mention that timber does not have that good a U value, and the above method would have been preferable from the start.
To provide some protection to the insulation you should consider using a flat roofing grade PIR which has a pre-treated suface, then either as you go or at the end of the install, use some duck tape to seal over the joints.

On a personal note, I would say that having a floor void in such an exposed location is not a very good idea, as the draft blowing underneath the floor will introduce a 'wind chill factor', you reckon you have -25C at times, well the wind chill factor would reduce this figure even further.

Therefore my comment (as I do not give advice) would be to seal up the perimeter edge of the building with a dwarf wall of some description, include some air bricks to provide a minimal amount of cross ventilation, I believe (but I will stand corrected) that these should be spaced at approximately 2m centres (single brick size should do the job) and if needed put in a couple of access doors on the least exposed side/s of the building. Any draft would be minimal and is unlikely to have any detrimental affect to occupants. As a caution I would mention that introducing the vents will provide ventilation to the void and ensure that no stagnant air develops which could otherwise bring on the start of timber decay!

If, its not one thing its another, hence the need for detailed planning and control of such projects at an early stage.

Regards

 

[Nige F]

No one wants to build a vent duct then

 

[alittlerespect]

Well! Nige F

I guess some people in particular ABCwarrior would much prefer to live without a vent, but how long they would live for would be subject to conditions, conditions that may one day be outside of their control.

Familiarity as they say breeds contempt not is a nasty way, but once ABCwarrior or his family get into the habit of blocking up the vent and opening a window for ventilation, probability has it that one day they will either consider that there is no longer a need to open the window (because things have been fine for so long) or more the case they or a visitor perhaps will forget to open the window. And that may be the last time that the individuals in the room see daylight!!

This is a known risk with wood burning stoves and gas fires, or at least I assume wood burning stoves are a known risk! And the whole purpose of putting the fresh air vent/s in is to save lives.

The fact that the vent blows a howling gale is unacceptable and is an issue that ABCwarrior needs to bring up with the Architect.

Regards

 

[mointainwalker]

@qlittlerespect

You keep repeating the dangers of woodburners. Do you have any actual experience of them ?

Gas and wood are very different. The fumes from gas are odourless and invisible and put you to sleep and then kill you..

If you have inadequate air supply , you are going to have poor/no real combustion and the result will be smoke. This can also be deadly but is not likely to escape from the fire (I find your negative pressure scenario unconvincing ) and apart from this, smoke would make you cough in the very unlikely event that it escaped into the room.

Searched but found nothing about wood-burner deaths, so i have difficulty in believing that too.

This is a known risk with wood burning stoves and gas fires, or at least I assume wood burning stoves are a known risk!

I think that is an assumption too far.

And the whole purpose of putting the fresh air vent/s in is to save lives.

i don't think so. I believe it is primarily to enable clean combustion and a good fire for heating.

 

[ABCwarrior]

Thanks for all the replies- the floor vent is next to the fire which sits on a caithness slab hearth- Thing is is that I can't really feel any positive pressure into the house when it's up to temperature so not sure if it's even working?! The idea of sealing up below the house is really just to slow down the air speed below it, and ply seems cheapest. The architect and builder seem to think what has been done will work but unless we get another winter of such extreme weather it cold be many years before we find it's not working. I know that burning partially seasoned or green wood is a CO risk and we have been avoiding that(hmmm....why don't we have a CO detector fitted from new then?). Another thing I have done this weekend is fit draught excluders to the bottom of all the downstairs rooms (fairly big gaps due to cheapish laminate flooring) which has drastically reduced the flow of air under the doors and into the rest of the house (mainly an issue if someone had been for a poo, opened the window when another was open in the house and the air gets blown through the house... )

It's a shame about the pipes cos the rest of the house does work pretty well- having the house on stilts was an idea they came up with to provide houses in areas with difficult gradients/soil etc

If it doesn't work this winter I'll be diigging my way under the house and doing it properly with insulation and a wall
It may just be luck but of the 4 identical houses built one did not get frozen pipes, and they had crammed logs etc below the house to season so maybe the air speed/volume reduction would be enough? Or maybe the joiners didn't have the DT's that day?!!!

 

[ABCwarrior]

Oh forgot to mention the pipes they fitted have some white plastic coating and are crimp fitted weird looking things so a current can't be run through them, supposed to be good for not bursting down to -60!!!!

 

[mointainwalker]

The reason not to burn burn green logs or partially-seasoned because they will burn very slowly, give out little heat and DEPOSIT A LOAD OF TAR IN YOUR CHIMNEY.

Should be 12 -18 months old and seasoned/air-dried.

 

[alittlerespect]

Hi!

The tape provides frost protection to hot and cold water services in exposed locations which might otherwise be subject to freezing.

There must be a thermostat connected to the pipework somewhere alongs its run and the unit must or rather should be connected to a mains electrical supply.

If you want further information do a web search on 'trace heating tape'.

Regards

 

[mointainwalker]

@alr

You are developing habits of not answering questions.
What about questions i posed earlier ?