I'm not familiar with the scottish regs but in England there are several ways to meet them. First is to use standard U-Values for walls and windows and keep the area of windows and doors to 25%. Other ways to show compliance exist. For example you can put extra insulation in the walls, ceiling or floor to compensate for extra glass (eg your 35%). There is no requirement to stick to 25% glass if you know what you are doing.

It's not trivial to calculate how much extra insulation you need in the walls to compensate for extra glazing. Basically you need to work out the area weighted average U-Value for the whole extension and show that it's at least as good as a similar building that uses the standard u-Values and only 25% glass. I suggest you work the numbers for both cases to see how far adrift you are.

If you can't install more wall insulation it might be possible to put in more floor or ceiling insulation or better sealed units in the windows instead to get the area weighted average down.

Posted By: jimshall I gather there are a lot of people renovationg outhouses round here who don't bother applying for a building warrant.

Can make it harder to sell your house if the surveyor/buyer asks to see the warrant.

Just to clarify, have you got the warrant or has the application yet to go in? If the previous guy issued the warrant then I would have thought that you were OK. If not, then you will have to meet the new regs (http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards). If you do it without a warrant then I would assume that you just store up trouble for when you come to sell.

Thanks for the advice. I have put together a proposal with fully detailed calculations to show that I can meet the maximum permitted heat loss by applying thicker insulation to the walls and roof. Hopefully our new building standards officer will approve them. It will cost a lot of money for the extra PU insulation and only save a few Watts per Kelvin but its better than blocking up a door. Probably the payback time in terms of heating cost and CO2 emissions will be ridiculous.

The previous building standards officer I was dealing with told me he was happy for me to get on with the building work last summer even though he had not issued the warrant. He required only minor ammendments to my drawings/plans in the application. That officer had taken months to deal with my application and at the end of the summer had still not replied to my final ammenments. I then found he had left his job and I was transferred to a new officer who is very helpful but more rigorous.

The legality of improving your home seems to be difficult to ascertain. Does anybody know have a link to reliable and coherent information on what work is notifiable in Scotland?

Neither our house nor the outbuilding I am restoring have a building warrant so I don't see the problem in improving them without a warrant. If we wanted to sell there wouldn't be a warrant anyway. The outbuilding was used as a backsmith's workshop many years ago and we are still going to use it as a workshop , albeit as an art studio, yet we have to meet building standards that are the same as a dwelling. We could have put up a conservatory with all glass that would be losing far more heat than the renovation I am doing, which makes a nonsense of the 25% rule. Also if the workshop could be considered as part of the dwelling then I would be well within the 25% rule ( the building meet at one corner) though the house would not meet the standards....

http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/homeinfo/faq

In particular this has a section on "Works that don't require a warrant".. In general most extensions other than conservatories are likely to need a warrant...

http://www.scotland.gov.uk/Resource/Doc/217736/0105338.pdf

jimshall,

you've done the right thing in showing that your building's heat loss is less than / equal to the "notional 25% building" heat loss. I have an extesion which was 47% openings to floor area, and submitted 2 little spreadsheets showing ...floor/walls/ceiling/ windows/doors.....the Uvalues fo each of these...and the related heat loss. The total heat loss was less than the "notional", the Warrant was approved - no problems.

GreenPaddy

The only thing I'd like to add is a warning to forum users based upon my experience with this matter is not to rely entirely upon the building standards officer giving accurate feedback on whether your plans meeting the regulations (and then act upon the advice). I have done this, having submitted detailed drawings and gone ahead with doing some of the renovation work without a warrant, based on verbal feedback and advice from an officer who was being helpful and no doubt acting in good faith. There will be many keen non-building professionals like myself who cannot afford to hand over a project to an architect and builder/s and who need to do some or all of the work/designs themselves. Also I'd like to express my gratitude to the participants and initiators of this forum.

As I was taught the day I started work in a planning consultancy, when it comes to local authorities "it isn't rocket science but if it is important write it down". Words have stuck with me since!