New build - Thermal block query

Ashevlin

My sister is undertaking a new build. She has had energy spec etc all done in advance. Engineer is on board too.
Something she has observed on the drawings is a thermal block base course to all inside walls and inner leaf of external - the house is a block build.
Her worry is that the house has a hollowcore first floor and that possibly the thermal block could be a weak point.
She queried with the engineer and he said its a requirement and that the thermal blocks are similar strength to normal blocks and he also said that the wide inner leaf being used is overly designed if anything.
From my side, I figured they could possibly be omitted as she is installing a plasterboard liner internally - but then I thought of the internal walls - they would still need the thermal block to kill the cold from the floor slab.
Any comments?
Are thermal blocks used in all cases even with hollowcore & where liner board is used.

Metric Tensor

1. The thermal blocks are subjected to the same load tests as the "standard" blocks so the engineer is 100% correct to say they are the same strength as normal blocks. (N.B. There are also some thermal blocks that have a lower load rating but provided the correct ones are used there should be no problems.) There is one proviso and that is if there is an area of the house were so call "structural" blocks are being used. This is exceedingly uncommon in a domestic setting so unlikely to affect your sister but her engineer will advise.

2. It's a poor detail to use dry-lining boards unless there is an air-tightness layer or two coats of plaster behind it. If you need extra insulation it should really go in the cavity - this frees up the inner leaf of blockwork to be a thermal store, ensures the dew point is within the cavity, makes air-tightness detailing much easier and should be cheaper too!

3. On a slightly more general point: The use of thermal blocks in this scenario is to stop a cold bridge forming. It is quite a common practice across the country now. I'm not 100% sure a cost benefit analysis would show it to be the best energy saving item to spend your money on but I could be corrected by someone with more expertise as I have not personally carried out thermal bridging calculations both with and without the thermal block.


So to sum up ... in my opinion:

Get rid of the dry-lining, that should be your main concern, not the thermal blocks.

Poor Uncle Tom

Ashevlin wrote: »

My sister is undertaking a new build. She has had energy spec etc all done in advance. Engineer is on board too.
Something she has observed on the drawings is a thermal block base course to all inside walls and inner leaf of external - the house is a block build.
Her worry is that the house has a hollowcore first floor and that possibly the thermal block could be a weak point.
She queried with the engineer and he said its a requirement and that the thermal blocks are similar strength to normal blocks and he also said that the wide inner leaf being used is overly designed if anything.
From my side, I figured they could possibly be omitted as she is installing a plasterboard liner internally - but then I thought of the internal walls - they would still need the thermal block to kill the cold from the floor slab.
Any comments?
Are thermal blocks used in all cases even with hollowcore & where liner board is used.

Presuming the engineer for the job has all the necessary information and expertise to make his statement, what basis are you making yours on? Just curious.

overshoot

Ignoring the potential cost/savings of the blocks. The thermal break in the wall stops a difference in temperate at the floor junction. In our damp climate that stops a condensation point and mould risk.
This wasn't an issue 10 years ago due to lower all round insulation/air tightness regs.
She will never be able to change this detail in future. Do it right now, its penny pinching in the wrong place.
... And while your at it... As mentioned above, put all the insulation in the cavity. Your plaster board gives the same risks

B-D-P--

I cant add more to the above but agree with it all.

Thermal blocks dont carry and drawbacks except a little more on price, but add alot to the build

BryanF

But under doors/screens go for foam type as fixing to the quinlites is problematic

sydthebeat

BryanF wrote: »

But under doors/screens go for foam type as fixing to the quinlites is problematic

kilsaran do a thermal block which is much more workable

i have ceased specifying quinnlites because of their workability issues.

Metric Tensor

Roadstone do a thermal block now as well.

Both Kilsaran's and Roadstone's are only about half as good as the Quinnlite from a thermal conductivity point of view but are much more like a standard concrete block when it comes to workability.

The Quinnlite is a lot lighter though so in circumstances when weight/loading is an issue you can build more/higher with the Quinnlites.

BryanF

Foamglas and similar are the job, but pricy

Corkblowin

Compacfoam is a much better product for under doors and floor-ceiling windows. Same u-value as foam glass but much more robust, can be fixed in to, and can be cut to the width of the ope (within reason of course). Used it on a job recently and won't be going back to anything else!

BryanF

Corkblowin wrote: »

Compacfoam is a much better product for under doors and floor-ceiling windows. Same u-value as foam glass but much more robust, can be fixed in to, and can be cut to the width of the ope (within reason of course). Used it on a job recently and won't be going back to anything else!

Have some at the moment, u-value not as good as foamglas but very sturdy & easy to cut/fix

Lumen

Corkblowin wrote: »

Compacfoam is a much better product for under doors and floor-ceiling windows. Same u-value as foam glass but much more robust, can be fixed in to, and can be cut to the width of the ope (within reason of course). Used it on a job recently and won't be going back to anything else!

Compactfoam has E fire rating, which as far as I can tell means "lightly fire retardant".

Foamglas is A1.

Is it not a problem having such a vulnerable base course?

(forgive the stupid amateur question, I'm just curious)