New Floor Construction - Acceptance and Figures

[johnobirches]

Hi All,
Trying to get the refurbishment and extension of our old cottage (not listed) in Lancashire underway.

Really struggling with the inter-relationship and requirements of/for builders, architects, building control, planners, structural engineers etc. Never mind the likes of energy consultants who seem to be coming out of the woodwork.

One issue at the mo is the floor. It's flagstones on earth and we want to have a floor structure as shown on p118 of the Old House Handbook i.e. 150mm LECA, breathable membrane, then 100mm limecrete with LECA slab, then heating pipes in a 75mm lime/sand screed. Flags to go back on top.

Trouble is we have no calcs for the thermal performance of this set up and have just been told by an architect this morning that Building Regs still call for a waterproof layer to be installed.

Has anyone got around/over these problems and can point me to some document or whatever that I can quote back at these people.

If I can't give thermal figures for the floor it seems BC may require silly depths of insulation under the roof/ceiling and so on.

All these so called professionals just seem to want to tick boxes and don't seem to want to consider anything other that the latest norm in construction techniques. Sorry ranting now.....
Thanks
John

 

[Roger H]

Hi John. Your architect isn't correct in assuming this is necessary.

Under building control 'Part L' listed buildings, scheduled monuments and buildings in conservation areas are expressly exempted from the requirements. Paragraph 3.8 in both Approved Documents L1B and L2B also give special exemption to locally listed buildings, traditionally constructed e.g. pre 1919, buildings and buildings in national parks and other historically important areas. Therefore your thermal provisions should be accepted regardless.

If they are trying to get you to install a membrane under Part C' (Resistance to moisture') you only need to have made 'reasonable provision to prevent the ingress of moisture'. If it is an existing flagged on earth floor, you have clearly improved on the existing situation both thermally and in terms of potential moisture penetration (It is certainly no 'worse' than the existing situation.

Have a look at this as regards ‘Part L’
http://www.english-heritage.org.uk/publications/energy-efficiency-historic-buildings-ptl/eehb-partl.pdf

 

[johnobirches]

Just the sort of info I was looking for.
Thank you so much Roger for the swift reply.
John

 

[AMc]

There are also provisions within Part L1B that can be used to reduce the amounts of insulation required where they would significantly reduce the living accommodation or would be so expensive as to fail to achieve payback within a set time using a simple formula. The Regs are here, you need to become familiar with them for your own sanity as you will get a lot of conflicting and inaccurate advice.
http://www.planningportal.gov.uk/buildingregulations/approveddocuments/partl/approved

Building Control officers are not necessarily experts in thermal efficiency. If you can demonstrate that your proposed insulation mechanisms have been tested to meet certain U or R values then they will be happy.
Look for documents from the manufacturers of the materials.

You can also go for a more complicated method of compliance if you can use a "green heating" system (heat pumps, biomass etc.) & insulating beyond PartL1B in your extension and a Whole House Assessment using SAP.
Essentially if you can demonstrate that your proposed plans will have a better overall performance than meeting the regulations for each thermal element of a similar sized property with a conventional heat source then you can proceed on that basis.
This will require some work from your architect and probably a paid report from an expert in SAP to give you the calculations for the notional building and proposed building.

I would fit as much insulation as is practical, heating is going to get more and more expensive and the type of work you're doing is only done under exceptional conditions. I wish I'd spent (even) more on insulation in certain parts of my renovation.

 

[MdB]

This will require some work from your architect and probably a paid report from an expert in SAP to give you the calculations for the notional building and proposed building.

My building control officer accepted my own SAP calcs generated from a SAP calculator I downloaded off the web. Admittedly we were a factor of 3 improvement in performance over what we needed to be so even if I didn't get every detail right we would still have been ok. This may have allowed him to accept it as ok.

 

[AMc]

Hence the "probably"

My paid consultant helped us to get the plans to within the tolerances which they originally didn't - that was worth his fairly reasonable fee. He also managed to accidentally produce two TERR reports (or was it DERR?) instead of one of each.
When I challenged this several months later, I was told it costs money each time the software produces a report and he didn't want to run them again to get the right header on the PDF. As my approval went through unchallenged, with the wrong headings, I'm not sure the BCO did anything other than note I'd paid for a SAP consultant & reports, was employing a reputable builder and experienced heating company and assumed it was OK.

I'm not suggesting my BCO wasn't good at his job, I consistently over specified the insulation when we actually fitted it and he was diligent about checking we'd installed what was expected. I think the complexity of the regs now makes it very difficult for an inspector to be an expert in all fields and in the same way he trusted my structural engineers calcs, he trusted a qualified expert to have done his job.