Recently had Planning permission come through for an extension to our old Welsh cottage. Still waiting, however, for the Buildings regs to be approved. Received the drawings from our architect on Friday with all the various materials to be used etc, I have not yet signed this though as there are one or two details which I am not quite happy with.

PVCu gutters have been specified on the plans, yet I have recently had some brand new gulvanised metal gutters added to my property and I wish to have the rest of the property fitted with the same quality gutters. Also Jeld-wen or similar PVCu windows have been specified, yet, if I can afford it, I would like wood framed windows throughout. Celotex / Cetotex has been specified for between rafters and mineral wool or quilt for batts of partition walls. Yet I wish to have Pavetex used and mineral wool is not a particularly pleasent material to work with and, quite apart from other considerations, I wish to save my builders from the misery of working with the stuff ! I do not wish to be responsible for poisoning my builders with ingesting any toxic materials, so it is organic paints, varnishes etc, wherever possible.( incidently, at formation level, proprietry weed killer has been specified, is there any environmentally frindly alternative to this ? ) I wish to have the external walls lime rendered and yet Lime has not been specifically refered to in the Building regs.

Do I need to return these plans to my architect to insert the specifications that I want ? I do not particularly wish to do so as this will waste time and money both of which are at a premium. I have been told by someone who regards himself as somewhat of an authority on the subject that it is not important to declare these minor changes and that building inspectors will not be bothered if I digress from the exact materials cited. Yet is there a risk that the building work might have to be undone if I use alternative materials ? My cottage is completely isolated, so there are no neighbours to complain about what I do with my cottage, but just how pedantic can these building inspectors be ?

Personally given the number of changes you want I would go back to your architect and have him update the drawings. Not so much for the Building regs but for your builders to quote against and work to. Remember these drawings will form part of your contract with the builder. If you send out drawings with a long list of corrections not only are mistakes more likely but it will look like you are a fussy customer. No builder really likes changes half way through the project and you have half a dozen before it's even started. Lets say a mistake is made and the builder bases his quote on the drawing not the correction. Even if it's his fault it will sour the relationship if you hold him to his agreed price. From then on he will be trying to recover the loss by cutting corners elsewhere. The changes your propose shouldn't really take the architect more than an hour to do.

Building Control won't care particularly about the changes to the gutters or windows (as long as the windows are reasonably standard size and design). They will be more interested in the insulation. I don't know anything about Pavetex and couldn't immediatly Google any. Is that the right spelling? You would need to check you can use the same thickness as Celotex and still achieve the required U-Values. Got a URL for Pavetex?

I agree with Fred. Our BCO was very helpful - we had a window that was slightly too narrow to act as fire escape. Only discovered it after it was built. Would have cost thousands to fix due to oak structure. The BCO proposed uprating the interior door instead.

Sorry for misspelling, Cwatters, Here is a URL
Will return later for comments ......

http://www.pavatex.co.uk/warum_pavatex.aspx

A quick look at the Pavatex data..
http://www.natural-building.co.uk/PDF/Pavatex/Pavaroof/Roof_PAVAROOF_PITCHED.pdf
..suggests they recommend a "warm roof" construction: 150mm deep rafters with 60-100mm Pavatherm above the rafters and wool/cotton between the rafters (achieves a U-Value of 0.2 to 0.17). That might mean a design detail change if the Architect has specified a "cold roof" design with Celotex between and under the rafters. Probably a trivial but the level of the rafters might need to change depending on how the extension roof connects to existing buiding.

I've no idea how the cost of Pavatherm and cotton/wool insulation compares with Celotex.

What wall construction has been specified? Cavity wall with Celotex in the walls?

Anybody any idea how "environmentally friendly" sodium chlorate is? It seems to me that a fairly simple compound which is water soluble and which breaks down in the process of doing its thing shouldn't do too much long-term harm.

I used it clearing an area of brambles at the top of my rather steep garden. The replacement grass grew well enough and the existing lawn downhill from it didn't seem to mind. You just have to be careful that your trousers don't explode. Really:

http://en.wikipedia.org/wiki/Exploding_trousers

Sodium chlorate "will turn shock-sensitive if contaminated with organic materials." http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc11/icsc1117.htm

Hmm, so weedkiller *or* shovel ("Just put the digger in over there, Mr Builder...")