Insulation - New Build

Duffers11

Hi, looking for advice on insulation. Have opted for 150mm external insulation on our new build. The house is built in 9" cavity. Was also considering putting 25-50mm insulated board internally. Reading some posts on here, I've read that it's best not to insulate internally also because of the heat release from block. Is there any sense in this, surely if a block was insulated both sides it would be better? Excuse my lack of knowledge with this one, just looking for best and most effective way to this this? Thanks

Outkast_IRE

Duffers11 wrote: »

Hi, looking for advice on insulation. Have opted for 150mm external insulation on our new build. The house is built in 9" cavity. Was also considering putting 25-50mm insulated board internally. Reading some posts on here, I've read that it's best not to insulate internally also because of the heat release from block. Is there any sense in this, surely if a block was insulated both sides it would be better? Excuse my lack of knowledge with this one, just looking for best and most effective way to this this? Thanks

My view on this would be if you have external insulation and no internal insulation then the result is you have alot of thermal mass on the interior of the insualtion which can be viewed as a good thing as when you turn off the heating etc the blocks etc should be releasing some heat into the home for a while afterwards.

If you insulate internally and externally you dont have the same thermal mass so although you would get quicker response times from your heating etc, it might not be as good for feeling warm when the heating is turned off. Also reading alot about the internal insulation at the moment about mould growth potential behind it etc im not convinced its the best solution in all scenarios.

Anyone feel free to correct me on anything i said.

Duffers11

Yeah I thought that, but from what I had read. I didn't know if they were referring to a solid block or cavity. We have a cavity block, I also read that in this instance the block would heat up and the warmth would escape through the gap in block and rise to ceiling, however we intend to cap the insulation at ceiling thus creating an envelope of insulation, ie no gaps or bridges. From what I would think, this would then keep the warmth in the block! I don't know if 150mm external would suffice and no internal?

Outkast_IRE

Duffers11 wrote: »

Yeah I thought that, but from what I had read. I didn't know if they were referring to a solid block or cavity. We have a cavity block, I also read that in this instance the block would heat up and the warmth would escape through the gap in block and rise to ceiling, however we intend to cap the insulation at ceiling thus creating an envelope of insulation, ie no gaps or bridges. From what I would think, this would then keep the warmth in the block! I don't know if 150mm external would suffice and no internal?

Are you getting professional advice on this , cause honestly getting a pro to sort out the details for you could save a fortune of money long term by eliminating cold bridges etc through proper detailing.

MicktheMan

Duffers11 wrote: »

Hi, looking for advice on insulation. Have opted for 150mm external insulation on our new build. The house is built in 9" cavity. Was also considering putting 25-50mm insulated board internally. Reading some posts on here, I've read that it's best not to insulate internally also because of the heat release from block. Is there any sense in this, surely if a block was insulated both sides it would be better? Excuse my lack of knowledge with this one, just looking for best and most effective way to this this? Thanks

Why not get 200+mm ewi instead of splitting the insulation layers.

Where/how will you place the windows in respect to the external insulation to eliminate thermal bridging?

How do you plan on making the walls, roof, windows and their junctions airtight?

How will you ventilate the house?

How do you know you will be in compliance with partL?

If you can answer these questions then great. If not (or not yet thought about) then perhaps you should get the advice from an experienced professional now rather than when its too late.

fclauson

get a pro involved

mixing you insulations between outside - the cavity and internally will lead to problems

they key item is know where the dew point will be and hence where condensation will happen

lets make this easy
inside wall is at 20deg outside is at 0 - somewhere across that will be the point at which condensation will form - you want this to be as far to the outside as possible
just EWI - it will be some where in the middle of the insulaiton - so not much of a problem
with full fill cavity it will be mid cavity - so again generally not much of a problem but can be an issue around windows
with a bit on the out side and bit in the middle and a bit on the inside you will need to get a proper calc done to make sure its where you want it

Duffers11

Thanks for the reply, it seems as though it's best then to go with just the external insulation. We are fitting it ourselves, buying materials only, the company we are buying from will call to site before purchasing and provide additional recommendations. We cannot afford to pay fitters but having said that have heard alot of stories about fitters and when it's your own it'll always be done to best standard possible. The only thing I was concerned about was the block being 9" cavity and the EWI it's not going to be filled or anything ya no so hoping it should satisfy!!

fclauson

what gurentee/warenty will you get if you fit it yourself

this has to last 30,40,50,60,70 years and if damp gets behind the insulation or its not fitted right then its useless

Do not skip and the start of your build

I would suggest if you are trying to keep costs down the a wide cavity is better as there are no specialist skills required (regular block layers can do the build, normal plastering etc)
BUT get the details around the windows resolved earlier - this is a typical area which takes time and can be difficult