Wrong lintels used - mould risk ?

[bmj1]

Hi all,

 

We're at ridge level now, which is super exciting... however, I've hit a bit of a snag when reviewing progress to date.. we've had some material substituted by the main contractor to use regular cavity wall galvanised steel lintels, instead of the hi-therm/insulated. We've now paused all progress on site while we review state of play.

 

My question is as follows:

 

- Putting aside all the impact on thermal performance, and SAP, etc, which we can compensate for (and live with), in practice, how much of an issue is this likely to be in terms of causing mould ? If this is a problem, is there a solution that doesn't involve replacing all the lintels ?

 

Many thanks in advance.

 

Edited April 21, 2023 by bmj1

[Mr Punter]

The Hi Therm lintels have a fairly long lead time and are quite a bit more expensive.  I can't work out from the picture what has been used.  If they used a separate lintel for inside and outside leaf they will be just the same thermally, but just more effort to build with.

[nod]

I’m supposed that your contractor has agreed to stop I think your being picky 

[Miek]

Fill the void with insulation,  'foamed in' PIR would be my choice. 

[Brickie]

You could use insulated plasterboard all the way round the opening,to mitigate the cold bridge. 

[PeterW]

Looks like a pair of lintels there - can’t see the stickers properly. As long as the SEng is ok with substitution then insulating the gap (PIR foamed and trimmed) will be better than the standard EPS inserts anyway. 
 

Also seems to be an additional Concrete lintel on the inside - what’s going on there or is that a very deep reveal ..??

 

Mould risk..? Zero if you’re ventilating correctly.

[Iceverge]

If its a separate pair of lintels then it should be thermally superior. Just make sure the bit between is well insulated. 

[Temp]

Is the top shaped to form a cavity tray?

[bmj1]

Thanks all. To be clear it is a single galvanised steel cavity lintel, so there is bridging straight across the cavity. Psi value is ~0.55, so it's material on the SAP.

 

It's deep reveals. 150mm cavity.

 

Plan is for whole house mvhr.

 

Keen for your follow up comments. Thank you!

 

@Mr Punter @nod @Miek @Brickie @PeterW@Iceverge @Temp 

[bmj1]

Lintels are the design of the attached (not this brand), i.e. the steel slopes towards the outer leaf.

[Iceverge]

I wouldn't worry too much about the mold. So long as it's not behind something that prevents airflow, like fitted furniture.Especially if you have MVHR. 

 

If your contractor has substituted the lintels on every window and they had clearly been specified as thermally broken I would be expecting them to find a solution to fix the problem. 

 

If you have say 20m of lintels at a PSI of 0.55W/mK Vs a thermally broken lintel at 0.05W/mK that's an additional heat loss of about 20m X 0.5W/mK X Dt20deg or about 200w extra peak heating load. 

 

I don't know how this fares in your overall scheme but it'd be 14% extra for our (passive) house. 

 

 

 

 

 

[PeterW]

That is extra load on the assumption there is no internal insulation though and it’s exposed ends. 150mm cavity isn’t close to passive levels so it’s probably negligible and not going to get any impact on SAP - air tightness score will be the biggest impact with a build like that. 

[Dave Jones]

agree with others said, not a biggie. Insulated plasterboard.

 

[Temp]

Think I'd cut blocks of PIR and use expanding foam to fill behind/around them.