MHRV when contractor won't agree to an airtightness level

Blisterman

Looking at having an existing property completely gutted and rebuilt with new wall and attic insulation, new concrete floor slab as well as a two storey extension.

The design is based around having Mechanical Heat Recovery Ventilation throughout the entire house, primarily for indoor air quality and comfort with saving money on heating a secondary concern.

It's been out to tender, and the contractor I'm most happy on going with has put the caveat that, since it's an existing house, they don't believe they will achieve the specified air tightness of 2 m3/hr/m2, and that they will not agree to any specified level.

I'm hoping that it will still be a reasonably air tight build. What I'm wondering is, am I wasting my time proceeding with a MHRV system? Will it still provide a good indoor air quality?

MicktheMan

Blisterman wrote: »

It's been out to tender, and the contractor I'm most happy on going with has put the caveat that, since it's an existing house, they don't believe they will achieve the specified air tightness of 2 m3/hr/m2, and that they will not agree to any specified level.

:eek::eek:
This would be of major concern to me and a major red flag. If the contractor cannot achieve a decent level of airtightness after a complete gut or indeed agree to any minimum level then I wouldn't choose that contractor. Period.

MVHR requires a decent level of airtightness so "hoping" to achieve reasonable airtightness is, imo, v risky. Keep looking, good contractors are out there. 2 m3/hr/m2 is readily achievable if you know what you're doing.

ec_pc

In my experience, some builders have not moved with the times and do not fully understand how to make a house effectively airtight or else they are perhaps too lazy to pay such attention to detail.

Keeping a very close (daily) eye on the builder is they way I achieved a high level of airtightness and I queried absolutely everything. I suppose I did test the builders patience at times, but it's my money and my house!

BryanF

It depends on how extensive the renovations are.

1. Op were design drawings and spec prepared?
2. What did the builder price from drawings & spec or Bill of quantities?
3. Was there a tender clarification meeting to discuss your concerns and ask how the Preformance criteria could be achieved?