insulation

slanemc

Hello ,

I am currently refurbing a 3000sq ft 1980’s bungalow. The walls are 9” hollow block. It is at the stage now where I need to commit to insulation and air tightness strategy. I would appreciate any comments below on the plan, as not really experienced at this. The present state of the building is that all internal walls have been removed, the whole floor has been re-laid with underfloor heating pipes and new concrete screed. All the inner faces of external walls have been given a sand and cement scratch coat.

Insulation:
I intend to internally insulate the external walls with 82.5mm insulated plasterboard, fixed to 1” timber battens. I am planning to run the electrical cables and domestic plumbing between the battens behind the insulation.
The building will have a cold attic. Plan to but 150mm rockwool between and 150mm above ceiling joists


Air tightness:
Plan to fix airtight membrane to underside of ceiling joist and tape to scratch coat on external walls
The existing ceilings are fairly high so was going to counter batten the ceiling and run as many of the services as possible below the air tight membrane to minimise number of penetrations.
Seal scratch coat to floor with airtight tape
Tape around windows and doors with airtight tape



Some of the concerns I have are:

- Because of the service cavity behind the insulation the airtightness barrier is essentially outside the thermal envelope, is this a major issue?
- Risk of condensation/Maintaining the vapour control barrier of the insulated boards.


This is a high level summary but would appreciate any comments to see if I am doing anything majorly wrong or suggestions of how do it differently.

west79

slanemc wrote: »

Hello ,

I am currently refurbing a 3000sq ft 1980’s bungalow. The walls are 9” hollow block. It is at the stage now where I need to commit to insulation and air tightness strategy. I would appreciate any comments below on the plan, as not really experienced at this. The present state of the building is that all internal walls have been removed, the whole floor has been re-laid with underfloor heating pipes and new concrete screed. All the inner faces of external walls have been given a sand and cement scratch coat.

Insulation:
I intend to internally insulate the external walls with 82.5mm insulated plasterboard, fixed to 1” timber battens. I am planning to run the electrical cables and domestic plumbing between the battens behind the insulation.
The building will have a cold attic. Plan to but 150mm rockwool between and 150mm above ceiling joists


Air tightness:
Plan to fix airtight membrane to underside of ceiling joist and tape to scratch coat on external walls
The existing ceilings are fairly high so was going to counter batten the ceiling and run as many of the services as possible below the air tight membrane to minimise number of penetrations.
Seal scratch coat to floor with airtight tape
Tape around windows and doors with airtight tape



Some of the concerns I have are:

- Because of the service cavity behind the insulation the airtightness barrier is essentially outside the thermal envelope, is this a major issue?
- Risk of condensation/Maintaining the vapour control barrier of the insulated boards.


This is a high level summary but would appreciate any comments to see if I am doing anything majorly wrong or suggestions of how do it differently.

Personally I am not a fan of the insulated plaster boards at that thickness. If it was my job I would chase the existing walls put in the electric ducts and grout up. Then fix 100mm 1.2 x 2.4 kingspan or xtratherm to the walls and tape joints on your wall insulation. Then tape your membrane on the ceiling to the wall insulation. Then slab over the wall insulation breaking all the joints. Also note if you have good ceiling height you should insulate the floor. If you don't a lot of the above is a waste of money

MicktheMan

slanemc wrote: »

1.- Because of the service cavity behind the insulation the airtightness barrier is essentially outside the thermal envelope, is this a major issue?
2- Risk of condensation

1. Rule of thumb; airtight barrier should be on the warm side of your insulation. As you describe it, you are doing the exact opposite.
2. Bigtime

Have you considered ewi?

spleonar88

Hi,

I am in the process of researching insulation for my retrofit. Am looking to install a Geothermal heat pump into the house, but want to make sure that the insulation is adequate before i embark on this, as i heard that bad insulation will be counter productive to the geo.

So basically, the insulation is looking like this for the minute:
100mm outer block
60mm kingspan insulation
100mm inner block
500 internal slab

Attic:
300mm fibreglass
12mm plasterboard with skimcoat finish

Floor:
75mm cement and sand screed
100mm kinngspan insulation
Radon Barrier on 50mm sand blinding
150mm subfloor
200mm hardcore

Any ideas of BER ratings and whether this would be suitable for a geo?

Thanks in advance

air

spleonar88 wrote: »

So basically, the insulation is looking like this for the minute:
100mm outer block
60mm kingspan insulation
100mm inner block
500 internal slab

How are you putting 60mm of kingspan in the cavity if it's a retrofit.
In any case the wall buildup you've proposed doesn't even come near to current building regulations.

spleonar88 wrote: »

Attic:
300mm fibreglass
12mm plasterboard with skimcoat finish

You'll need to cross lay and ideally use something to support the upper layers to go to 300mm with fibreglass.
Why not put 50mm of kingspan to the underside of the joists, tape and foam and then put the plasterboard on top. The kingspan will help with airtightness also.
Another thing than can be done is to put a vapour open but wind tight membrane over the attic insulation. This helps avoid draughts under the eaves (essential for ventilation) from stripping away heat.

spleonar88 wrote: »

Floor:
75mm cement and sand screed
100mm kinngspan insulation
Radon Barrier on 50mm sand blinding
150mm subfloor
200mm hardcore

Again won't meet regs and is totally insufficient for geothermal. I wouldn't put it in without at least 200mm under the slab.
What's the plan with the subfloor? If it's a 150mm concrete slab it sounds strange to put sand blinding on top.

spleonar88 wrote: »

Any ideas of BER ratings and whether this would be suitable for a geo?

Impossible to estimate the BER rating as there isn't near enough information to go on. No, it's not suitable for geothermal in my opinion as you have proposed it.

Honestly I think it's time to get an experienced professional - architect and / or engineer involved in the project.

spleonar88

Thanks for the feedback. I am just quoting from my plans. I have very limited knowledge on this matter. Interesting that you say it won't meet current building reg, Ill have a chat with my engineer later on. Any more advice would be great so i can go back to him and talk about it

air

No problem.
Are you rebuilding sections of the house perhaps? This would help explain the reference to cavity wall insulation.
People could help out more if you give a better description of your project and what you want to achieve with it.