Thickness of new cavity wall

[bobpatrick]

Hi guys

Can I ask if anybody knows how I can build the thinnest cavity wall to meet the required regs.

I am building a new lounge, and bedroom extensions on my single storey property.

The existing outside wall is faced concrete blocks which are about 100mm, with a 50mm cavity, and thermalite blocks on the inside wall.

I will of course be using faced concrete block to match the existing, but want to keep the overall wall thickness to the minimum.

The floor will have to be Block & Beam due to ground levels.

Any ideas if there is a super insulation, or new way of doing this.

I have had a problem with the build due to a drain that was 2.6m deep, running across where the footings go, so have had to go for mini piling (expensive believe me) had estimates ranging from £6000 to £17000 plus vat !!!

Also, any idea on how much I should be paying for a bricky to build the walls? One extension is 3.5m x 4.5m and the other is 3m x 5.5m

Thanks

 

[^woody^]

An inner timber frame can achieve an overall thickness of 240mm including plaster

Otherwise its about 285mm including plaster with masonry

 

[bobpatrick]

I'm not keen on timber frame (to old i think, like things solid ).

Is it better to have 'full fill' of 'partial fill' for the insulation?

 

[JamesNorton01]

It depends on whether the wall needs to compensate for any other elements, specifically if the new windows and doors are more than 25% of the extension plus are of any covered up by the extension.

But, assuming not, 285 is about right; you'll need a U-value of 0.28, in masonry that would be:
100 block, 25 cavity, 50 Cel@tex, 100 block, 15 plaster:

Monkey around with this:

http://www.celotex.co.uk/Other-Resources/U-value-Calculator

Depends a tiny bit on block density and whether dot and dab or not

but don't forget the bit I first said...

 

[^woody^]

There is no "better" as they achieve the same result.

Your considerations should be the ability of the builder to do a partial fill wall construction well, and the overall effect of the wall thickness (and choice of internal block) if using full fill

 

[JamesNorton01]

If you ask R@ckwool they will advise full fill, if you ask Cel@tex they will say partial.

Rigid foams ask for min 25mm cavity, wool can be full fill but even with the cavity the rigid urethane foams perform better thermally per unit thickness, but are more expensive.

Another issue is that rigid foams can be installed v.poorly and with air flying around the cavity the performance can be massively reduced because of thermal bypass - ie the warm air gets around the insulation, where as mineral wool fully filled is harder to go wrong and is less likely to be effected by this.

J

 

[noseall]

I agree with James N in the sense that a partial fill wall built poorly will have an effect on the wall performance, particularly from the point of air leakage.

Unless there is a zealous foreman cracking the whip over the brickies, i can't see them obeying all the robust building details, as with the window fitters, roofers, plasterers etc, because all these trades need to pay particular attention when closing the cavities, fitting insulation, adding sealant etc.

From a builders' point of view, full fill cavity walls are simple to build and are easier to get right.

 

[Perry525]

A super insulation is made by Aerogel.
One centimeter = four inches of polystyrene or similar.
Aerogel are increasing their production and are hoping to expand into the home building market.
It is expensive!

 

[noseall]

A super insulation is made by Aerogel.
One centimeter = four inches of polystyrene or similar.
Aerogel are increasing their production and are hoping to expand into the home building market.
It is expensive!

Is it licensed and approved i.e. BBA?

 

[Perry525]

A super insulation is made by Aerogel.
One centimeter = four inches of polystyrene or similar.
Aerogel are increasing their production and are hoping to expand into the home building market.
It is expensive!

Is it licensed and approved i.e. BBA?

========================
Its good enough for moon walking and walking in space.
You are allowed to use products that exceed their spec.

 

[JamesNorton01]

Eye wateringly expensive....

J

http://www.aerogel.com/Aspen_Aerogels_Spaceloft.pdf

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9&page=1

 

[geraint]

I agree with James N in the sense that a partial fill wall built poorly will have an effect on the wall performance, particularly from the point of air leakage.

Unless there is a zealous foreman cracking the whip over the brickies, i can't see them obeying all the robust building details, as with the window fitters, roofers, plasterers etc, because all these trades need to pay particular attention when closing the cavities, fitting insulation, adding sealant etc.

From a builders' point of view, full fill cavity walls are simple to build and are easier to get right.

I find that the lazy bricklayers would rather do a full fill and then walk away... as usual.... Far easier than cutting celotex...

Again, surely with the current regs you must use the ****e cavity closers
as a return in blockwork or brickwork or it would not meet the current regs...

 

[mointainwalker]

++

A super insulation is made by Aerogel.
One centimeter = four inches of polystyrene or similar.
Aerogel are increasing their production and are hoping to expand into the home building market.
It is expensive!

It is extremely expensive and I didn't think it could achieve 10: 1 over PSX - any l/inks to that Perry525 ?

 

[noseall]

I find that the lazy bricklayers would rather do a full fill and then walk away... as usual.... Far easier than cutting celotex....

I agree.

So why complicate things by insisting on partial fill when there is a simpler method, that is difficult to get wrong and achieves the same result.

Not all bricklayers are lazy, just that some are forced into a position where
laying large numbers of bricks/blocks means putting food on the table. Unfortunately quality can suffer as a result.

 

[bobpatrick]

This is all very interesting, thanks.

I had a look at the Aerogel site, and http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9&page=1

which had a link to http://www.proctorgroup.com/products/thermal-insulation/spacetherm

so will contact them next week, but would like to try and have the insulation in the cavity, and as small a cavity as possible.