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Sustainable Renovation in Practice Q&A

We answer your top questions from our recent webinar.  

Clive Bowman of Zero Waste Scotland, Chris Morgan of John Gilbert Architects and James Wilson, green builder on Skye, provided their insights on the questions raised at the end of our webinar.  The recording is available to watch online.

If you would like to discuss how your business or project could work with Zero Waste Scotland to receive specialist support and advice in this theme, please email the team.  More information on our Construction Industry Support Programme.


How can we make it easier to find contractors who will install underfloor insulation from above?

In theory a contractor will do what you ask them to, as long as it’s broadly reasonable, legal and compliant with regulations. General awareness and guidance is not always at the level needed, hence the guide and problems you’ve faced.

Are statutory building regulations supporting circular economy construction materials any closer?

Not yet, but work is under way through a number of channels including by Zero Waste Scotland and ACOM, to integrate embodied carbon into building regulation.  This will result in a need to choose lower embodied carbon (whole life) materials.

How do you avoid standard renovation making things worse? Can you ask for better if it goes wrong?

Often, the problem we face is that previous work is ‘compliant’ but is actually pretty poor, hence the need for the guide and improvement in regulations and general practice.  Most of the guide is an attempt to avoid the problems of merely ‘compliant’ work which is in practice not adequate.

As a practice, how do you fund post-occupancy evaluation - do the clients pay for it?

There are lots of different ways, some are funded by clients we’ve worked with before and who have seen benefits of doing so. Some funding bodies will support it (for example, Edinburgh World Heritage funded lots of good POE on current listed tenement refurbishments on Canongate).  It’s much easier to get clients to pay if they’ve already seen the benefits.

How can the divide between planning and building warrants be overcome when improving energy efficiency so interventions don't have consequences on historic fabric?

Integrated thinking is a big issue for all large organisations.

Where does the statuary responsibility for cavity walls lie?

That’s a very tricky question. There is a guarantee scheme (CIGA).

What does Chris thinks about refurbishment of non-residential?

The principle is the same on the whole but there is far more variation in types of internal use and therefore internal conditions and problems.

Is there a guide for how to avoid thermal bridging when retrofitting with interior insulation?

I think there is a BRE document and there’s lots of guidance on Google. It’s the main work we spend time on in design because it’s not always easy and compromises and analysis, taking time to resolve. All Passivhaus information is also good on thermal bridging, even if not related to retrofit.

What is the panelists' view on Passivhaus methodology in assessing and delivering proven new and retrofit projects?

It’s almost always very good. It’s not a perfect system, but the benefits outweigh the disbenefits by some margin, and I say that as someone who was (and remains) pretty skeptical. Also using PhPP and other methods from Ph doesn’t mean you have to reach the target levels, just that you have better tools to get better results.

Is there a solution you have found satisfactory between natural ventilation and MVHR?

Good question, and not really, because MVHR is pretty full on – take it or leave it. Having said that there is plenty of cheap and not very good MVHR which fits that description, but I wouldn’t recommend it.  As long as ventilation works well, it should always deal with moisture and IAQ effectively, so remaining question is if you want heat recovery. My own view is that even when airtightness levels aren’t reached, MVHR is useful in that it recovers heat, warms, and dries out air which is useful in Scotland where most internal air tends towards being too humid.

Does the report/your research compare the breathability of natural Vs synthetic insulation materials?

Yes, albeit not directly or all the time, but it’s certainly a critical part of most of the recommendations.

Should a wind tight membrane have breathability or be waterproof?

It’s always permeable to moisture, the question is how permeable to air. Most breather membranes also let in quite a lot of air, whereas some are specifically meant to be airtight (whilst also vapor permeable). No it should not waterproof.

Does a loft 'cavity wall' include 'kit homes'?

The cavity wall and kit homes are totally different.  ‘Cavity’ is term for masonry cavity both leaves.  ‘Timber kit’ is timber internal frame and masonry (usually) on outside of cavity – very different solutions, all are covered in the guide.

How do you achieve best balance between using materials with low embodied carbon and good efficiency?

It depends on the situation – with time running out for zero carbon, low embodied energy materials save carbon now, so are increasingly important, but both are obviously critical now.

What's your opinion on ventilation for buildings in 3 to 5 air permeability levels that don't officially need MVHR?

For me the benefits of high efficiency, warmer, drier air more important than fairly minor efficiency loss due to infiltration.  However, others might not agree. I think views are changing on this though.

Does upgrading from original Victorian style glazing to double glazing (16mm) still provide useful ventilation?

If using same frames, you’d probably want thinner double-glazed panels.  16mm is ‘normal’ double glazing, for example Fountainbridge glazing in Edinburgh, I think their panels are about 8mm or similar.  Ventilation is unaffected as you can still open the sash and case.

What percentage of renovated houses in your study deviated from the expectation of SAP and EPC?

Most of them but not all have studies showing exactly that.  In most studies I’m aware of RdSAP underestimates energy consumption most, SAP does also, but less so. SAP is often accurate on modern buildings because much better suited.

How can we ensure that some of Rishi Sunak's Green recovery fund will go into natural sustainable insulation materials?

Increased recognition of the higher embodied carbon of unnatural materials is a driver for this.  

Will there be any companies specialising in natural insulation methods registered as Government approved installers?

Zero Waste Scotland is currently putting forward proposals for natural low carbon materials to be an essential aspect of the Energy Efficiency Programme.

What's your view on the sprayed underfloor insulation?

It’s very complicated, on the whole it’s not great, but clearly has some advantages. We have investigated a couple.

Do you think the EnerPHit standard could become more common in renovation projects?

Yes.  It’s really not that hard in my view, but I do understand not possible in some cases. Getting close still an option.

Can PIR internally work ok in your experience?

Yes, it depends on the situation. I wouldn’t use it where moisture movement is important but, for example in already non-breathing construction, or in relation to a concrete slab etc, it should be fine if good ventilation also in place.

On the wall details - what is the green tape shown on the details?

One of the robust / expensive German tapes for example Tescon by Pro clima or similar by Siga, others are also available.  

Can we get sight of the four-page Policy Guidance?

It’s available on The Pubble Trust website.

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