advice on insulation spec

Spudnik73

Hi

I am in the drsign phase of a 3000 sq ft build. My architect has provided come back to me with the insulation specs and I would be grateful for some input. He is proposing a 120mm cavity. Our goal is to achieve a high level of insulation which will reduce ongoing heating bills.

Wall Insulation: Xtratherm Thin R cavity wall (80mm) in the cavity with 37.5mm Xtratherm Thermal liner on the inside wall.

Floor: Xtratherm Thin-R Underfloor (125mm)

Ceiling insulation: Mineral fibre 150mm between joists 150mm over layered to underside with 42.5mm Xtratherm XT/TL Liner

We are building a 1.5 storey house which is c. 3000 sq feet.

Any feedback would be greatly appreciated.

Thanks

LoTwan

Don't forget rafter insulation. Half of your upstairs walls are actually the roof. Strongly consider a warm roof construction, I wish I had.

I would put 150mm in the floor, purely because you will never get another chance to increase the insulation in your floor.

fclauson

Spudnik73 wrote: »

Hi

... He is proposing a 120mm cavity. Our goal is to achieve a high level of insulation which will reduce ongoing heating bills.

Wall Insulation: Xtratherm Thin R cavity wall (80mm) in the cavity with 37.5mm Xtratherm Thermal liner on the inside wall.

What do you mean a 120mm cavity - but then only puttting 80mm of insulaiton into it ?

and why are you insulating the two sides of the inner block - you would be better off putting more into the cavity and leaving the internal block as thermal mass

You should also check where the dew point forms in your wall make up

Francis

bravojohnny

Have you seen Xtratherm's new cavity insulation; its called CavityTherm2011.

They claim that you can use this new product in a 100mm cavity, the insulation board is 95mm thick & only requires 5mm air cavity.



I have no ties with xtratherm I only mention them as I have seen the OP had.

Best of luck with the build!

imitation

bravojohnny wrote: »

They claim that you can use this new product in a 100mm cavity, the insulation board is 95mm thick & only requires 5mm air cavity.

On paper it sounds good. In reality your going to have to get your block layer to lay the blocks perfectly even and to scrape away excess mortar (which probably excludes a fair few fellas initially). Then they'll have to be vigilant to prevent mortar, gloves, crisp bags and all other types of rubbish from falling in there.

bravojohnny

^Sure thats the same advise you would give for all parial fill cavity insulation boards....

sinnerboy

Advice routinely ignored in the case of partial fill .

I doubt that full fill boards would work in practice.

Stop expecting blockies to do this stuff.

Spudnik73

Thank you all for your replies. Sinnerboy, I read the reference material with interest. The argument as i understand it is that partial fill cavity is no longer best practice and other methods should be considered.

To this end ( and as I am still in design phase) can you give some recomendations on what methods you might go with i,e, full fill cavity, maybe Timber frame?

Thanks

imitation

Personally I would keep with the cavity wall, I went with a 125mm cavity and 100mm board along with 40mm dry lining(yes I know what I said 3 posts ago Luck was on my side with my blocklayer). In my books cavity block are tried and tested, you don't want to be a guinea pig for some fellas 1st or 2nd try off a ICF/Timberframe/etc house

Sadly your probably fast learning that almost nobody has the same opinion on what's "best". All you can do is weigh up the pros and cons of each choice.