Waterworks Posted December 29, 2019 Share Posted December 29, 2019 I'm in the early stages of planning an off grid small one room open plan cabin style house in the UK , not really subject to any extremes of weather, i want to base it on a passive house style of insulation where the absolute minimum of fuel is needed to heat it, I'd like to find what thickness of PU foam board is the practical maximum , I'm aware that the thicker you go there are diminishing returns, as far as I know now this is in the region of 300 mm ? Link to comment Share on other sites More sharing options...
SteamyTea Posted December 29, 2019 Share Posted December 29, 2019 Hello Do you have any weather data for where you want to build? Knowing those parameters can help a fair bit, takes the guess work out of it, and solar radiation can add a lot of energy to a place (ask @Jeremy Harris). Also, a small place has a larger surface area to volume ratio, this is a killer when it comes to designing a low energy building, just too much wall.. The physics id pretty basic, two parts, the insulation reduces the power (the watts) that go though the wall, but once though, air movement sucks more power out. This is why there are a two parts to complex construction formula. First thing to look at is the R-Value of materials (make sure you pick the SI ones and not the funny American ones). The K.m2/W. Also air tightness is important, no point having a foot of insulation if there is a window open. Link to comment Share on other sites More sharing options...
joe90 Posted December 30, 2019 Share Posted December 30, 2019 Location also makes a difference, we are in a windy location not far from the sea in a damp environment, @Jeremy Harrisis in a protected hollow so has a warmer micro climate. Not sure how you measure that but it makes a difference. Link to comment Share on other sites More sharing options...
A_L Posted December 30, 2019 Share Posted December 30, 2019 Hello, IMHO there is nothing to gain by going below a U value of 0.1W/m2.K for any fabric element. Assuming no thermal bridges (e.g. rafters) this occurs at 250mm (or slightly less) for most PUR/PIR products (e.g. Celotex). The money would produce a greater financial and environmental benefit invested in renewables/air tightness/efficient appliances etc 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted December 30, 2019 Share Posted December 30, 2019 22 minutes ago, A_L said: The money would produce a greater financial and environmental benefit invested in renewables/air tightness/efficient appliances etc Or a very fuel efficient car. 24 minutes ago, joe90 said: Location also makes a difference, we are in a windy location not far from the sea in a damp environment, @Jeremy Harrisis in a protected hollow so has a warmer micro climate. Not sure how you measure that but it makes a difference. Possibly a correlation between low level windspeed and temperature at the site. May also be a place to do a Covariance analysts with irradience. Link to comment Share on other sites More sharing options...
scottishjohn Posted December 30, 2019 Share Posted December 30, 2019 (edited) 21 hours ago, Waterworks said: I'm in the early stages of planning an off grid small one room open plan cabin style house in the UK , not really subject to any extremes of weather, i want to base it on a passive house style of insulation where the absolute minimum of fuel is needed to heat it, I'd like to find what thickness of PU foam board is the practical maximum , I'm aware that the thicker you go there are diminishing returns, as far as I know now this is in the region of 300 mm ? 150mm of pir will be eqvilaent to 300mm of most other types --no need to go any further --just make sure the living area is an air tight box,godd tight fits ,no gaps --job done you want to go another step then foam backed plasterboard to finish you could build it from thick SIPS panels+ cladding on outside ? depending onsize you could uase SIPS for roof as well air tight is as important if not more so than insulation thickness--if you letting the heat out or cold drafts in your peeing into the wind forever 300m pir is OTT Edited December 30, 2019 by scottishjohn Link to comment Share on other sites More sharing options...
Jeremy Harris Posted December 30, 2019 Share Posted December 30, 2019 23 hours ago, Waterworks said: I'm in the early stages of planning an off grid small one room open plan cabin style house in the UK , not really subject to any extremes of weather, i want to base it on a passive house style of insulation where the absolute minimum of fuel is needed to heat it, I'd like to find what thickness of PU foam board is the practical maximum , I'm aware that the thicker you go there are diminishing returns, as far as I know now this is in the region of 300 mm ? You can easily compare the various forms of insulation performance by looking at the thermal conductivity of each, usually given as λ or lambda. If you want to do some rough and ready comparisons, ignoring thermal bridging and edge/geometric effects, then this simple U value calculator may be of use: Simple U value calculator.xls There are some typical λ values given in that spreadsheet as starting points, but you can usually find the exact value for any particular product from the manufacturer's data sheet. As a general rule, the thickness needed will be directly proportional to the λ value, so PIR with a λ of 0.022 W/m.K that is 200mm thick will be equivalent to rockwool, with a λ of 0.037 W/m.K that's 337mm thick. Link to comment Share on other sites More sharing options...
Waterworks Posted January 20, 2020 Author Share Posted January 20, 2020 I thinking about building a small cabin in some remote woodland I will own, my thinking is that insulation is relatively cheap and at the planning stage is easy to factor in as much as you want, i could then cut the wood fuel use for heating down to a level that just an area of coppice ( x acres ) on site will support indefinitely. Were not going to live there but were going to stay there way longer than is legal, unless we get found out. I've read tales of passive houses that require no heating at all most of the UK year. Link to comment Share on other sites More sharing options...
Temp Posted January 20, 2020 Share Posted January 20, 2020 Remember not all thicknesses of PIR is available, will probably need multiple layers. Some thicknesses will probably be cheaper per mm than others, especially if you are using stocked thicknesses rather than special order thicknesses. Link to comment Share on other sites More sharing options...
Russell griffiths Posted January 20, 2020 Share Posted January 20, 2020 I would think that if you insulate it too well you may find the woodburner unbearable to have lit how big is the cabin? we are fitting woodburners into cabins that we rent out, but they are badly insulated, I think if I increase it too much the occupiers will probably need to keep the door open. We have a woodburner in the house we live in now and find that with the oven on also on a Sunday evening we have to open the back door to let some cold in. Link to comment Share on other sites More sharing options...
Tennentslager Posted January 20, 2020 Share Posted January 20, 2020 49 minutes ago, Russell griffiths said: I would think that if you insulate it too well you may find the woodburner unbearable to have lit how big is the cabin? we are fitting woodburners into cabins that we rent out, but they are badly insulated, I think if I increase it too much the occupiers will probably need to keep the door open. We have a woodburner in the house we live in now and find that with the oven on also on a Sunday evening we have to open the back door to let some cold in. Exactly this... Link to comment Share on other sites More sharing options...
Waterworks Posted January 24, 2020 Author Share Posted January 24, 2020 I would suggest that excess heat can always be vented away but not visa versa, maybe the wood burning stove in the winter would only need to be tiny, but that's not a problem I can see as it frees up time spent processing fuel. Link to comment Share on other sites More sharing options...
SteamyTea Posted January 24, 2020 Share Posted January 24, 2020 4 hours ago, Waterworks said: maybe the wood burning stove in the winter would only need to be tiny Evan a small woodburner is hazardous to health. On 20/01/2020 at 21:22, Russell griffiths said: we are fitting woodburners into cabins that we rent out Taking a bit of a risk in my opinion. Link to comment Share on other sites More sharing options...
Russell griffiths Posted January 24, 2020 Share Posted January 24, 2020 1 hour ago, SteamyTea said: Evan a small woodburner is hazardous to health. Taking a bit of a risk in my opinion. According to our letting agents, a woodburner is the biggest selling point in the English holiday rental market, the second is a hot tub. Link to comment Share on other sites More sharing options...
SteamyTea Posted January 24, 2020 Share Posted January 24, 2020 2 minutes ago, Russell griffiths said: According to our letting agents, a woodburner is the biggest selling point in the English holiday rental market, the second is a hot tub. Seems odd with the known health hazards (of both). Do you allow smoking in your holiday lets? Link to comment Share on other sites More sharing options...
Russell griffiths Posted January 24, 2020 Share Posted January 24, 2020 (edited) 7 minutes ago, SteamyTea said: Edited January 24, 2020 by Russell griffiths Link to comment Share on other sites More sharing options...
Russell griffiths Posted January 24, 2020 Share Posted January 24, 2020 9 minutes ago, SteamyTea said: Seems odd with the known health hazards (of both). Do you allow smoking in your holiday lets? In 35 years of doing one of the most dangerous jobs we have in this country, the thing I always considered to be the most life threatening thing I did every day was. Drive my car to work. I know we are saying woodburners are dirty, but c,mon we aren’t all dropping dead because we sat by the fire in the pub last night. 1 Link to comment Share on other sites More sharing options...
Cpd Posted January 24, 2020 Share Posted January 24, 2020 7 minutes ago, SteamyTea said: Seems odd with the known health hazards (of both). Do you allow smoking in your holiday lets? Wood burners etc...... This is one of those situations where there is a clear line in the sand and some people are firmly on one side with placards and reams of information and the others are in there comfy chair with a single malt watching the flames flicker..... Let’s not get to bogged down on this subject every time it comes up..... reminds me of thermal mass....... Link to comment Share on other sites More sharing options...
SteamyTea Posted January 24, 2020 Share Posted January 24, 2020 6 minutes ago, Russell griffiths said: but c,mon we aren’t all dropping dead because we sat by the fire in the pub last night. Not how it works, it is an accumulation. 3 minutes ago, Cpd said: Let’s not get to bogged down on this subject every time it comes up Trouble is, like a lot of risks, people need constant reminding. Why we have road signs and health warnings alcohol. Link to comment Share on other sites More sharing options...
joe90 Posted January 24, 2020 Share Posted January 24, 2020 Some people still smoke cigarettes despite the known risks!!! Link to comment Share on other sites More sharing options...
SteamyTea Posted January 24, 2020 Share Posted January 24, 2020 6 minutes ago, joe90 said: Some people still smoke cigarettes despite the known risks Yes, as I do. But we are very restricted as to where we can smoke them. Link to comment Share on other sites More sharing options...
joe90 Posted January 24, 2020 Share Posted January 24, 2020 5 minutes ago, SteamyTea said: Yes, as I do. And as you know I have a wood stove ( I know which I prefer) ? 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted January 24, 2020 Share Posted January 24, 2020 Just now, joe90 said: I know which I prefer Have you cured the air leak on the inlet pipe yet? Link to comment Share on other sites More sharing options...
joe90 Posted January 24, 2020 Share Posted January 24, 2020 4 minutes ago, SteamyTea said: Have you cured the air leak on the inlet pipe yet? yes mate, all sealed up, got some more caulking to do around windows and would not mind another air test, but not at £250 . Just the MVHR to balance, just need someone to help me ? Link to comment Share on other sites More sharing options...
SteamyTea Posted January 24, 2020 Share Posted January 24, 2020 2 minutes ago, joe90 said: Just the MVHR to balance, just need someone to help me Let us know when, I have the first 3 days of the week free at the moment. Link to comment Share on other sites More sharing options...
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