Thermal Block Not Used on Internal Block Walls

[Gaf]

New build. Due to a pipe needing moving, leading to the screed and ground floor insulation needing removing, I noticed the thermal block specified on the construction drawings wasn't laid for the internal walls. I got to visit the site when the thermal blocks were laid on all external walls and they are definitely there.

 

Attached shows the construction drawings. The floor makeup from top to bottom:

 

• Concrete screed with underfloor heating 75mm
• Kingspan Thermfloor TF70 125mm with perimeter strip 25mm
• Concrete subfloor (A 193mesh) with 50 mm cover 150mm
• Monarflex RMB 400 d.p.m. radon barrier acting also as d.p.m.
• 300mm compacted hardcore filling

 

My understanding is the thermal block is supposed to support the thermal envelope of the house. Without these thermal blocks on the internal walls we now have a thermal bridge down to the foundations. I can live with a thermal bridge to some extent - trying not to get too wrapped up - but what troubles me more is that to my understanding this also likely creates a condensation point? Many of the ground floor walls will have built in units along them so we won't necessarily have easy access to keeping an eye on condensation - also just don't want to feel like I've to keep an eye on anything since it's a new build and the thermal blocks were included in the spec.

 

Am I being OTT?

 

Edited August 31 by Gaf

[JohnMo]

External wall if as per drawing are in the correct place.

 

But if the internal walls do not have them there will be a thermal bridge present.

 

Ask the builder how he is going to rectify?

[Redbeard]

Are you saying that the spec clearly states the internal walls should have a thermal block layer (but that it is not on the dwg)? You said

3 hours ago, Gaf said:

I noticed the thermal block specified on the construction drawings wasn't laid for the internal walls.

 

...and your external wall dwg indeed has an annotation showing the thermal block, but the internal wall dwg does not. If the requirement is stated in the spec then it seems unfortunate that it did not get transferred to the dwg. Day-to-day contractors are often more likely to read annotations on dwgs than the whole spec, whatever they should, in theory, do. Whatever the rights and wrongs, if the req't is in writing then you have every right to ask for a rip-out and replace. 

[Gaf]

@Redbeard Good point re: spec document vs drawings. The specification document supplied by the architect and included/supplied to the builder in the tender process states the following under 'Internal Walls': "Supply all necessary bricks / blocks, mortar, lintels etc. as required and erect internal block walling in accordance drawings (sic). All blockwork to be 7N/mm2 and to BS 6073, mortar to case (iii) of BS5628, density to be between 1200kg/m3 and 1500kg/m3. Finish as per drawings."

 

Just looking over all of the architect's construction drawings and it seems to be the case that he didn't 'repeat' annotations on the same pages where an item is repeated. Not sure if that's standard practice? For example, on the attached section d-d drawing, there are:

• Two foundations (left / right walls), but he only annotates one of them
• Two window cills (left / right walls), but he only annotates one of them
• Two thermal blocks at ground level (left/ right walls), but he only annotates one of them
• Two thermal blocks at the cills (left/ right walls), but he only annotates one of them
• Two Keystone lintels etc. etc.

 

On the drawing where the internal wall is included with what appears to be the different looking block (matching all of the other blocks annotated as "Thermal Block"), the thermal block is annotated in the same way as all the other drawings, only once (attached). Even though on the section d-d drawing, only the left thermal block is annotated I saw them laying the thermal blocks on the right side as well (even though it's not annotated).

 

[Mr Blobby]

If I were a builder reading those plans then I would have installed a thermal block on every external wall adjacent to the insulation.

 

The thermal bridge here will be significant enough to make me very unhappy if it was my house.

 

Mindful that thermal blocks cost ten bob more and bricklayers don't like laying them, I would ask the builder why they are not there and what he's going to do to rectify it.

 

Edited August 31 by Mr Blobby

[Susie]

Did you see the radon barrier going in across the compacted hardcore. 
some one on here can hopefully tell you how much of a thermal break this would be. 

[Gaf]

@Mr Blobby In fairness, they did install the thermal blocks on all external  walls, even where the thermal block wasn't specifically annotated - they seemed to pick up that where it wasn't annotated a second time, it was still required. It's the internal walls that are structural / run down to the foundations where they have not put in the thermal blocks.

 

@Susie I didn't see it going down but the building surveyor had to inspect it after it was installed for building regulations, certification, and sign-off. He's on holidays at the moment so can't get directly speaking with him for a while. The build-up is (top to bottom):

• Concrete screed with underfloor heating 75mm
• PIR 125mm with perimeter strip 25mm
• Concrete subfloor (A 193mesh) with 50 mm cover 150mm
• Monarflex RMB 400 d.p.m. radon barrier acting also as d.p.m.
• 300mm compacted hardcore filling

I can't see any reference to that particular DPM having thermal properties, maybe as you mentioned someone here may know?

[Mr Blobby]

8 minutes ago, Gaf said:

In fairness, they did install the thermal blocks on all external  walls, even where the thermal block wasn't specifically annotated - they seemed to pick up that where it wasn't annotated a second time, it was still required. It's the internal walls that are structural / run down to the foundations where they have not put in the thermal blocks.

 

Sorry I think we may have our wires crossed.  When I said external wall I meant the inner leaf of the 'external' walls around the perimiter of the house.  As opposed to the internal walls that separate rooms.

 

Are you saying that the builder installed a thermal block on the outer leaf of the external walls instead of the inner leaf?  Surely not.

 

Edited September 1 by Mr Blobby

[Gaf]

@Mr Blobby They installed the thermal blocks on the inner leaf of all the external walls. So the external walls all have the thermal block (on the inner leaf).

 

They didn’t install the thermal blocks on the single block internal walls. The image on my last post shows where they installed the thermal blocks (green) and where no thermal blocks were installed (red).

 

We have six internal block walls and all six are structural, so go down to the foundations. All six of these internal walls (not the inner leaf of the external walls) throughout the whole ground floor have no thermal blocks at all. 

 

[Andehh]

You win some, you loose some. Reality is the difference is negligible. Add a bit more insulation to somewhere else, and move on.  Accept your heating bill might be an extra 50p a month due to this over sight.

 

 

[Gaf]

14 minutes ago, Andehh said:

You win some, you loose some. Reality is the difference is negligible. Add a bit more insulation to somewhere else, and move on.  Accept your heating bill might be an extra 50p a month due to this over sight.

 

 

It’s not a heating cost issue to me. It’s a potential condensation issue.

[Andehh]

Isn't the house just built like any normal house? Few houses use thermal blocks.

[Gaf]

4 hours ago, Andehh said:

Isn't the house just built like any normal house? Few houses use thermal blocks.

Genuinely don’t mean to sound chippy but I have no idea mate. I don’t have a notion of what a ‘normal’ house is. I just know what our house was designed and costed to include. The contractor had his QS do the costings so I also don’t know if we paid for blocks that weren’t laid, personally I accept there can be some this done and won’t pick a battle over a few blocks from a cost perspective.

 

We spent a healthy chunk of budget on professional fees and time making certain decisions ahead of time so the builder wasn’t calling us asking for direction during the build. We have a building surveyor carrying out periodic inspections to check on the work meeting building regulations. For us, naively, we thought all our work ahead of time would mean once we pulled the trigger on a contractor it would be a fire and forget situation.

 

As mentioned, I don’t care if there’s a negligible heat loss issue. I can live with that. But I don’t want a condensation issue in a new house costing half a million. Our current 1970s built house has condensation issues with periodic (thankfully pretty minor) mould growth so I want nothing to do with condensation.

[Mr Punter]

Because the internal walls are a fair distance from the outside walls there will not be much heat loss and therefore the chance of condensation will be negligible.

[MikeGrahamT21]

Don't assume just because its not AAC that its not a thermal block, as they also come in medium dense which look like any other block: https://www.huwsgray.co.uk/lightweight-concrete-blocks/stocks-insulite-solid-breeze-block-100mm-73n-10609-2851049

 

Agreed they don't perform like AAC, but they're still classed as thermal blocks, with higher strength whilst keeping the budget low

[Gaf]

On 01/09/2024 at 20:48, Mr Punter said:

Because the internal walls are a fair distance from the outside walls there will not be much heat loss and therefore the chance of condensation will be negligible.

 

Like to come back with an outcome on posts. 

 

Got chatting to building certifier who said to leave it alone. Thermal blocks on the inner walls are “completely overkill” and will have no noticeable difference 

[Andehh]

Yep, I think he is right as well!