External Insulation for New Build

Ferocious

I’m finding it difficult to get good information on external insulation for new builds. I’m considering it as an option and I’m trying to weigh up the benefits and costs. It seems to be one of the more common construction methods on the continent where external walls consist of a block on flat with up to 200mm of external insulation. I have a couple of concerns/ presumptions /questions that you guys are probably able to put right...

External insulation is effectively ‘wrapping’ the walls in insulation so you are insulating/preserving the thermal mass of the walls which must be a benefit over timber frame or internal insulation systems? By the same token, would the house take longer to heat up since the same mass of the wall would absorb a certain amount of energy?

Can you apply thicker external insulation than you could in a traditional cavity resulting in a better U value?

A single 215 thick leaf is the recommended method but is this inherited from the continent where it may be colder but may not have the same issues with ‘dampness’ we have. Without a cavity, you are relying on the quality of installation/workmanship and integrity of the render + insulation to keep the inside dry? Is there anything to be gained or lost by building a cavity wall and externally insulating that? Outside of cost, I’m assuming insulation in the cavity plus external insulation would be overkill and bring you into the zone of diminishing returns?

Regarding costs, a single 215mm only requires slightly more blocks than 2 x 100mm walls. Should the block laying be cheaper – only one leaf with no insulation to be fitted? Apart for the cost of the insulation itself, are there any other major cost considerations?

Would the plasterer have to be specifically trained or need any special experince?

My knowledge here is limited so apologies if this is a bit long winded and some questions are a bit stupid but I think this is the place to find some of the most well informed opinions.

Ferocious

Anyone have any thoughts on this? Particularly in relation to the cavity wall versus the block on flat, both with external insulation.

sas

Ferocious wrote: »

Anyone have any thoughts on this? Particularly in relation to the cavity wall versus the block on flat, both with external insulation.

You can't use cavity wall construction behind external insulation. You are going to get air movement in the cavity and it will wipe out the effect of the insulation. If you check the SEI website you can see the passive house upgrade guidelines. For cavity wall houses they recommend that you pump the cavity (i.e. remove it) when externally insulating.

Ferocious

Thanks sas. Didn't see that on th SEI website.

sas

Its there because I found it recently. I can't find it today. I'll PM you if I find it again.

Builderfromhell

PLastering external insulation is a specialist job and it is unlikly any plasterer can do it.
I do not have time now to go into detail but specilaists will know how to deal with external taps, ESB or/and Gas meters, Window cills, Corners, Window jambs, Pipe and other service penetrations, Plinth etc.

BUILDERSKY

HI EVERYONE
the external insulation is better becouse
1,a dew point is moving out side the wall
2,cold bridges are eliminated
3,wall gets warm from inside and cumulate it, so it works like heat storage
4, house is realy warm when its done with a good workmenship

BUILDERSKY

and to do it you need someone with cert from system supplier,

BUILDERSKY

sas wrote: »

You can't use cavity wall construction behind external insulation. You are going to get air movement in the cavity and it will wipe out the effect of the insulation. If you check the SEI website you can see the passive house upgrade guidelines. For cavity wall houses they recommend that you pump the cavity (i.e. remove it) when externally insulating.

yes it has a sense.

external insul should be done up to roof plate level where meet a roof fnsulation for continiuation

obviously the best result is if you use a porotherm clay blocks insted concrete
(they have u-value 0,3 themself) then 4" polyuretan external insul

the worst way to insulate house is internal insulation.
why is not efficiant and it cos cancer (its forbidden in Germany)