325mm wall options

[Oz07]

Okay looking at a job where due to limited space max wall thickness is 325mm. 

Also electric will be only fuel source so ideally want low u value. 

Job is to be brick clad so 222.5mm available to make up wall.

Obviously slips onto some form of board would be better in a u value sense but let's keep it with brick face for now. Single storey if it makes a difference with regards to timber frame thickness. 

[Jeremy Harris]

If you have a brick outer skin then that will allow you to get away with using a low decrement delay insulation, so any closed panel system with a high performance insulation will give you a pretty good figure.  There are 190mm SIPs panels available now, I believe, and they are probably pretty good.  I doubt you need more than a 25mm ventilated cavity behind the brick skin if using a decent closed panel system.  Ideally pick something that's fairly cold bridge free, hence the suggestion of SIPs, as for walls they are better than a single frame timber structure, because they don't have all the cold bridging through the timber frame.

[Oz07]

Cheers will look into. As ever floor wall junc would need attention. 

Keeping cold away from sips bearing with around 25mm to play with

[AliG]

I can't really think of a system that will do better than SIPs in terms of U-value to wall thickness, especially if you want a brick outer skin.

Usually with a SIPs wall you are looking at a 25mm service cavity plus 12.5mm plasterboard on the inside.

A fairly standard buildup would be 100mm brick, 50mm cavity, 140-145mm SIP, 25mm service cavity and 12.5mm plasterboard, so around 330mm depending on the specific SIP panels. I think you might struggle to get a SIPs manufacturer to agree to a less than standard cavity as it might not be allowed in their BBA certificate for the warranty.

A wall like this would have a 0.19 U-Value. Not spectacular, but not bad. Much as people can obsess about it, the difference between 0.16 and 0.19 is likely to be less than 5% to overall energy use.

If the design allows no services on exterior walls then you can lose the service cavity and use a 170mm panel which would bring the U-value down to around 0.16.

Kingspan do a system using their 172mm panel and 25mm brick slips which would give a 0.16 U-Value on a 275m which wall including service cavity.

Much as people would want the lowest U-Value possible, in a single story house the roof and floor will be relatively more important for insulation. You could probably get the roof down close to 0.1 assuming there are no restrictions on thickness there.

To some extent it is a matter of compromise if the 325mm is an unavoidable restriction.

[tonyshouse]

140 block, not aerated, 200 eps, high tech tender, wet plaster inside

[ProDave]

What's the reason for wanting brick?  I specifically avoided brick or block and went for timber frame with external wood fibre insulation. My wall thickness is within your target and has a better U value, but you would have to settle for a render finish.

The issue for me, was with a timber frame and blockwork skin, the cavity has to be ventilated so it's open to outside air. So the brick or block skin is adding virtually nothing to the insulation at all.

[Crofter]

Dave: would your system take brick slips?

[tonyshouse]

My ideal amount of insulation in a wall is 300mm so I think a 325 thick wall is too thin.

[Jeremy Harris]

12 hours ago, AliG said:

A wall like this would have a 0.19 U-Value. Not spectacular, but not bad. Much as people can obsess about it, the difference between 0.16 and 0.19 is likely to be less than 5% to overall energy use.

 

The heating requirement difference between those two figures could easily be 30% or more, as there is a sharply non-linear impact on heating requirement with decreased U value.  By the time you get to a U value of around 0.1 there may well be no heating requirement at all, for example.

[AliG]

Fair point Jeremy, i was thinking of a house with relatively standard build. As you get closer to passive levels the percentages become very large although the absolute costs may be small.

Have you made your heat loss calculation available here? I found it very useful as you can use it to give you an idea of the effects of changing different parts of the fabric of the building and the cost benefit of doing so. Comparing better windows to better wall U-value for example.

[ProDave]

7 hours ago, Crofter said:

Dave: would your system take brick slips?

Honest answer I don't know, and I don't know who would know.