SIPS but no MVHR?

[sips novice]

Hi everyone. Hope you don't mind me reaching out. I'm not a self-builder (yet -though I'd love to be sometime) but am hoping to buy a house built by a self-builder and would appreciate some thoughts. The house is built using SIPS - and it's the first time this builder has used them. It is 3000ft2 and on the EPC it has an air tightness reading of 2.9m3. But there is no MVHR - just trickle vents, so I'm worried about air quality, condensation and mould (though there is none there visible currently).

 

I asked the guy why he didn't put in an MVHR and he said that he didn't want  the smells of BBQs from neighbouring properties being drawn in, and that the bathroom extractor fans have a background ventilation setting. He also said he put more windows in to ensure enough trickle vents. But I'm struggling to get comfortable with this because everything online recommends a mechanical ventilation system when you build with SIPS. Any thoughts appreciated. Thank you.

[Nickfromwales]

Are there comprehensive pictures of the house being built? The VCL would be my biggest concern, as ventilating internal spaces can be done later tbh.

[ProDave]

SIPS is one of the easiest methods to get correct and air tight so to get an air test of 2.9 seems like a lot of poor detail, or deliberate leaks?

 

To be honest the difference between 2.9 (needs mvhr) and 3.1 (does not need mvhr) is not significant.  I doubt you are going to get problems, especially if the bathroom fans have a slow constant speed.  But the house would have been better if he had tried harder and done the job properly.

 

You will no more get BBQ smells via mvhr than any other ventilation method, and they do have an off switch so if there was a rare case of a bad smell outside you could turn it off for a while.

[JohnMo]

25 minutes ago, sips novice said:

just trickle vents, so I'm worried about air quality, condensation and mould (though there is none there visible currently).

I would replace all trickle vents with humidity activated, then no one can sneak the vents closed, as normally happens. These stay a little bit open for background ventilation and as room humidity increases they open more. Make sure there are no trickle vents in wet rooms or kitchen, these will make the fans just draw from that rooms ventilation, not the whole house.

 

Make sure all internal doors have at least 5 to 10mm clearance at the bottom. This allows building cross ventilation with doors closed.

The fans in wet rooms should be almost silent, they should be set to building regs flow rates, and ideally automatically boost based on humidity, not via a switch.

 

Next ensure building is signed off as complete before handing over any money - or YOU could end up having to install MVHR to satisfy building control.

[Nickfromwales]

If a certain volume of air is removed from the property, the exact and equal amount of outdoor air will be drawn in to replace it, via whatever gaps or engineered openings (such as trickle vents) there are.

 

Smells from outside get into my house, same as any house, but with MVHR you get to shut it off in extreme cases whereas I’m bloody well stuck with it.

 

Builders are great…….😌 

[sips novice]

Thanks so much everyone for your replies. To answer the queries:

 

• no, no pictures of VCL during construction unfortunately.
• sadly no room to retrofit an MVHR as there is no loft space. But we could always change the bathroom extractors for better ones. 
• windows are by ID systems. Don't think they are humidity activated vents currently but good idea -  I could change them if I can find them colour-matched. 
• I reckon he must have been cost saving - but odd, because he chose to spend £14k on a bespoke front door...Priorities, priorities...!

Thanks again