Timber frame specs, advice please

Sticky toffee

I'm looking to order a timber frame house in the next week or 2 and have narrowed the search down to 2 companies after lots of research and twoing and froing. The house is a bungalow with attic conversion.
1st company are fairly new to TF and very cheap but my eng has been to look at their work and could not fault it. Spec is 140mm frame filled with frametherm 35, intello inside with a service cavity inside that.
2nd company are one of the best known in the country and do their own type wall. Their spec is 225mm wall with factory fitted 150mm fibreglass and 50mm rigid board. Inside that is the airtight membrane and inside that service cavity.
The price difference is 8k but the 2nd company is throwing in a hrv to sweeten deal. Now I have several dilemmas;
1) Insulation. I came across information recently which suggested that the rigid insulation is not effective over a long period of time as it contains gas and as the gas dissapates over time the insulation loses its effectiveness.
I looked at pumping company 1's frame with cellulose but there are some opinions out there who reckon its not a good idea putting damp cellulose into a timber frame.
2) I am reluctant to put in a hrv, it just doesnt sit well with me going to the expense and trouble of putting in this system just to have fresh air in each room but there seems no real alternative. Is it really worth the cost for both the airtightness and the hrv? Would it be a waste of time having airtightness and windows with vents?

I appreciate any informed opinions!

Juantorena

Re point #2...

Not sure if you have read much through this forum but I am in agreement with the popular philosophy of insulate the bejaysus out of the house, make it as airtight as you can and then see what your heating requirement might be. You're spending money up front to limit the heat losses and also to reduce your heating (system) requirements.

If you are building airtight MHRV may be necessary. Not sure about trickle vents in windows - either whether they would work in a very airtight house or how they would work with an HRV system though..

anybody home?

glasswool seems to be of preference in walls as it is easier to get a good fit than you get with rigid insulation.

Foils are being used to up grade glasswool u-values on timber frame to those kinds of values you can get (in theory) from rigid boards. At Ecobuild all the timber frame guys were using glasswools like frametherm with TLX Silver insulation.

Borzoi

Sticky toffee wrote: »

1) Insulation. I came across information recently which suggested that the rigid insulation is not effective over a long period of time as it contains gas and as the gas dissapates over time the insulation loses its effectiveness.
.

The dissapation rate is very slow - and the same thing applies to celulose.

Sticky toffee wrote: »

2) I am reluctant to put in a hrv, it just doesnt sit well with me going to the expense and trouble of putting in this system just to have fresh air in each room but there seems no real alternative. Is it really worth the cost for both the airtightness and the hrv? Would it be a waste of time having airtightness and windows with vents?

In a nut shell yes - air vents and airtightness are not compatible. If going for airtightness - use a MHRV, they are very efficient, and will paback in energy and air quality terms

sas

Borzoi wrote: »

The dissapation rate is very slow - and the same thing applies to celulose.

When the gas (pentane) disipates from the rigid boards it is replaced with air.

Where as cellulose only ever contains air. So air is replaced with air. No performance change.

What specifically were you talking about?

Borzoi

sas wrote: »

What specifically were you talking about?

My point was that all insulation degrades over time