Help needed for retrofit and extension silver standard?

[Anonymous]

We are renovating and extending a Victorian farmworker's cottage. I am the client pushing builder and architect towards aecb silver standards. We are using 150ml cavity with mineral wool insulation on the new extension. The old house is 9 inch solid brick wall. We are limited to internal insulation. First floor will go onto joist hangers and we will use a warm roof construction to produce a continuous insulation envelope. There is one load bearing internal wall which poses difficulties for insulation, so we are considering using insulation backed plasterboard at the wall to wall junction here. The floors have been dug up and we will use floor insulation. The current proposal for the old house is thinsulex silver and u values quoted 0.24 for walls and 0.18 for roof. I would like to use MHRV. We will use airtightness testing.
The building firm have good experience with traditional building but we are all finding the sustainable journey challenging.
Emissions-zero have offered some software modelling (for a fee) to help us progress.
I thought I would post here for guidance to the following key questions.
1. The builder is concerned about wall stability if he cannot do brick returns at reveals. This would be his routine with 100ml cavity and he does not think the building will be structurally as sound without these with 150ml cavity. Is the solution to this more wallties or can anyone offer any other solutions?
2. I have read a lot of articles about the risk of interstitial condensation when insulating old buildings. We are considering this at every turn but is it possible to be completely confident it won't occur?
3. I see passivhaus certified MHRV installers will ensure no dust in pipes, any pipes outside external envelope insulated etc, is there a list of these anywhere on site? (search option does not seem to be working currently)
4. We have a 4.5m section of glazing on exposed eastern aspect (southern aspect not suitable). The best folding door option available manages 1.4 u value. This has pushed us towards sliding doors, optiwin seem good, any other suggestions?
5. What, if any, software modelling should we do and how to go about it?
I appreciate this could have all been a lot easier if we had used an architect with experience from the start! On the plus side any eco champions amongst you have a good opportunity to educate!

[Anonymous]

Just looked at Viking House “breathing window”, anyone have any experience of this?

[Mark Siddall]

Dr J
I would agree with David. In response to your queries:

1. This is not even recomended solution for Building Regulations! (see pages 32-33 of this the Accredited Construction details (ACD) http://www.planningportal.gov.uk/uploads/br/masonry_cavity_wall_insulation_illustrations.pdf) ….NOTE: In terms of thermal bridging the ACD details are pretty shoddy compared to AECB details.
2. External insulation is your best bet at minimising these risks
3. Certified Passivhaus designers get training with regard to the performance requirements. There is no “Passivhaus certified installer” for MVHR systems. There is a course for trades that is just about to get off the ground.
4. Sliding doors can be leaky. I would advise that you get hold of test certificates demonstrating that the air leakage is less than 0.2 m3/m @100pa (easilt achieved by most windows)
5. Passivhaus Planning Package (PHPP) is used for Passivhaus, EnerPHit (Passivhaus retrofit) and AECB Silver. It has a proven track record so it is the one that I use and would recomend.

All the best,
Mark

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