Insulated slabs

cuculainn

Hi

I know this topic has been posted before but I am still looking for a definitive answer.

We have a new build. 150mm cavity that we plan to pump.

My question is should we also slab the internal leaf of the external walls with insulated slab?.

My OH wants to but I'm not sure of the cost/benifit.

Can anyone advise?

What will the U-value of the 150mm pumped cavity walls be?

Would Uvalue increase by much by adding the insulated slabs? 48mm?

I really dont want to be doubling up on wall insulation if there is no need


Any help appreciated

MicktheMan

You really ought to consult a professional.
How do you know you are complying with the building regs?
A good arch/tech/energy consultant will be much better able to advise re insulation, airtightness,ventilation,heating system & controls and take into account your lifestyle etc.

cuculainn

Thanks for the reply

We comply with all building regulations without slabbing the external walls.

However, alot of trades people and people who have built houses recently recommend putting insulated slabs on the walls.

I am looking for peoples input into the cost vs benifit of doing this or not doing this.

muffler

cuculainn wrote: »

I really dont want to be doubling up on wall insulation if there is no need

Never such a thing as "no need" unless of course you are just happy to meet the legal requirements and nothing over and above that which would be a shame.

You can never go wrong with additional insulation but I take your point if you feel it isn't necessary to pass the regs. But you really should look at it more from an investment point of view. Additional insulation will lead to reduced expenditure on heating costs.

What you really should find out is the "payback" time frame. At the end of the day you will need a BER assessor so I would suggest you get one now and he/she will give you details regarding the option of fitting insulated slabs.

There are a lot of factors to be taken into account so take your plans & spec to the BER consultant and they will explain in more detail what the benefits are and possibly the extra cost also.

kboc

cuculainn wrote: »

Hi

I know this topic has been posted before but I am still looking for a definitive answer.

We have a new build. 150mm cavity that we plan to pump.

My question is should we also slab the internal leaf of the external walls with insulated slab?.

My OH wants to but I'm not sure of the cost/benifit.

Can anyone advise?

What will the U-value of the 150mm pumped cavity walls be?

Would Uvalue increase by much by adding the insulated slabs? 48mm?

I really dont want to be doubling up on wall insulation if there is no need


Any help appreciated

Another option is to build the cavity at 200mm and use a soap bar on the internal leaf. This will give a good u value (theoretically anyway alot depends on your trades men and professionals minimising cold bridging) and don't put any insulation on inside/outside leaf. This will allow the inner walls act like a massive radiator, thermal mass it is called. You will probably need a structural enginer to spec cavity and wall ties.

good luck

MicktheMan

cuculainn wrote: »

Thanks for the reply

We comply with all building regulations without slabbing the external walls.

However, alot of trades people and people who have built houses recently recommend putting insulated slabs on the walls.

I am looking for peoples input into the cost vs benifit of doing this or not doing this.

And a lot of houses with internal slabbing that I test for airtightness fare poorly because they dont seal the blockwork behind the slabbing. Is thermal mass important for your central heating & control system? A good professional will discuss all these inter-related issues and come up with the best solution for you, not yer man down the road who built a house!

cuculainn

MicktheMan wrote: »

And a lot of houses with internal slabbing that I test for airtightness fare poorly because they dont seal the blockwork behind the slabbing. Is thermal mass important for your central heating & control system? A good professional will discuss all these inter-related issues and come up with the best solution for you, not yer man down the road who built a house!

Hey thanks for all the replies. The 200 mm cavity not an option. Already have150 mm
We will get the blockwork plastered before we slab for airtightness.
We have our engineer working on this too but just wanted to get the opinions of the resident experts on boards.