Cavity wall and Internal Insulation

jones.mark.p

Hi All,

I am new to this site so please bear with me. I am currently in the process of building my own home and rightly or wrongly I have contracted the job out to a developer. Everyone I speak to cannot stress enough the importance of insulation and the fact that this is the only chance I have to get it right.

People are telling me to ensure I
- place a 50mm insulated slab on all external walls.
- Slab on internal walls
- slab upstairs ceilings with a 20mm insulated slab
- slab attic ceiling with 37.5mm board

My builder tells me that I have 100mm insulation in the cavity and that this added insulation is a waste of money and I will not benefit from it. He assures me that with 100mm insulation in the cavity will give me that top level insulation rating when the walls are sand and cement coated and skimmed.

With all the information I’m getting I don’t know who to believe. I want to do the best job possible now and not be sorry later. Can you give me your opinions?

I have checked the kingspan, hytherm, SEI, environ websites for some technical documentation but cannot find anything. If it is the best but way to go then I would like to have some documentation to go back to my builder with.

Any websites / references would be appreciated.

Thanks in advance for your posts

sydthebeat

mark,

it would be my opinion that slabbing your inner walls with 'cosy boards' would be more trouble than its worth.
100mm in the cavity, if installed correctly is more than adequate.
The cosy boards will only serve to increase air leakage at openings and junctions unless you first completely skim the inner walls with at least 7-8mm fine sand and cement scratch coat.

Do you not have a construction professional ie Architect or Architectural Technician, working with you on this project??? Because thats the person you should be listening to.... and believing...

most definitely, do not slab internal walls..!!!! thats a lazy solution that should only be considered if your blockwork is absolutely terrible.....

ardara1

What exactly is the 100mm of insulation in the cavity?

the bolt

jones.mark.p wrote: »

Hi All,

I am new to this site so please bear with me. I am currently in the process of building my own home and rightly or wrongly I have contracted the job out to a developer. Everyone I speak to cannot stress enough the importance of insulation and the fact that this is the only chance I have to get it right.

People are telling me to ensure I
- place a 50mm insulated slab on all external walls.
- Slab on internal walls
- slab upstairs ceilings with a 20mm insulated slab
- slab attic ceiling with 37.5mm board

My builder tells me that I have 100mm insulation in the cavity and that this added insulation is a waste of money and I will not benefit from it. He assures me that with 100mm insulation in the cavity will give me that top level insulation rating when the walls are sand and cement coated and skimmed.

With all the information I’m getting I don’t know who to believe. I want to do the best job possible now and not be sorry later. Can you give me your opinions?

I have checked the kingspan, hytherm, SEI, environ websites for some technical documentation but cannot find anything. If it is the best but way to go then I would like to have some documentation to go back to my builder with.

Any websites / references would be appreciated.

Thanks in advance for your posts

at the minute im working on a site south dublin and there is 140 mm insulation in the walls and 50 mm inside,its timber framed .

Clarelassie

We are putting 60mm K8 in the cavity wall, but are also dry-lining inside - if you can afford it, it is well worth doing in my opinion. I am not an engineer so can't comment on u-values, just a fellow builder, but will describe it as I understand it, open to correction.

If you just have insulation in the cavity, you will spend energy initially heating the inner leaf of blockwork - this does store some energy which it can release back into the room. If you have it dry-lined, then the room will heat a lot quicker as you don't spend time heating up the inner leaf of the blockwork.

I would recommend that you talk to people that have built with and without dry lining ( we did) and the unanimous vote back was those that didn't put it in regretted it. It is a lot harder to retro fit the insulation if you change your mind later.

Because of budget concerns, we did lower our spec of dry-lining - would rather do that than remove it entirely. Best of luck with your choice!

daddycool

Just moved into our build - I believe the new property buzz is 'insulation, insulation, insulation' and so I agree with your concerns and post

People rave about costs, but done right, the payback is fast - over-engineering is never a bad thing here as any heat kept is energy saved (both morally good and for the pocket)

We didn't want to take internal space away, and also liked the idea of the inner leaf (of a masonary build) acting as a heat store (UFH powered by Hydro Geo Thermal)

We built a 200 cavity instead of 100 and put in 160mm of Kingspan (2 * 80mm bopards lapped). Also over-engineered the floor, ceiling and attic insulation (boarded the pitch up to the capping)

Now when we cook, the house overheats and we have to open a window, but the breeze is nice. The HRV unit means that even this heat is kept and circulated in the house. Ultimately do your research, and don't get too locked in to your builder, In my brief expereince of a self-build, a builder will usually take the 'easiest route' and simply be happy once the building regs are met (which in my mind are too low)

That's my tuppence worth ...

glencoe

Mark

Some links

http://www.planningportal.gov.uk/england/genpub/en/1115315126267.html

http://www.scanhome.ie/passive.php

http://www.passiv.de/07_eng/index_e.html

http://www.sustainability.ie/insulation.html

http://www2.dupont.com/Tyvek_Construction/en_IE/

http://www.mitsubishi-aircon.co.uk/ Lossnay

In short rigid insulation is better than quilt and the more the better.
Detailing is everything filling gaps and sealing all joints and junctions.
A well insulated and air tight building will be cheaper to heat, but you will need to allow for ventilation/heat recovery.

It will be cheaper now to spend the money now

sydthebeat

glencoe wrote: »

In short rigid insulation is better than quilt and the more the better.

while i would agree with all else youve posted... posting a glib statement like this is disingenuous and conditional to particular situations.