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Thanks woody, but my question is aimed specifically at the cavity only. I'm building the skins from 100mm concrete blocks, but believe that the cavity itself can vary in width and so to can insulation etc. I suppose I'm asking what the most common cavity and insulation width is for a cavity wall.

Hi guys, Can anyone tell me what the best cavity size is for a standar rear extension? I know that the lintels for example come in sizes for anything between 50 - 110mm. I'm keen to ensure I have as much internal space in the extension as possible, but don't want to compromise on insulation...

Maltaron, thanks for the response. Not entirely sure how this could be possible. The only place for an access chamber would be in the extension as it extends the width of the house. I'm already having to remove the manhole that is there because they are no longer allowed (at all) within a build...

My building control officer might be able to shed some light on this for me when I meet with him next week, but I thought I'd ask the question so I don't sound too clueless. The project is a single storey rear extension and at the same time I'm installing a downstairs toilet (essentially under...

Hi guys, Just trying to get my head around the floor construction for a single storey rear extension. I have decided to go with suspended timber floor. The outside ground level is about 300mm lower than the inside floor level is now. I assume my trench foundations will need to be 900 deep...

DRon, I was quite relieved to see your post, I'm in the process of starting an almost identical project of knocking down an existing lean to extension and replacing it with a new single storey extension within permitted development. Also planning to do most of this as a self build and have...

Thanks Oldun, I found another useful table online listing C16 timber for diferent purposes. Confirmed your numbers.

Thanks gents, will ask the architect to specify coorect joist sizes in his design, I just wanted to understand whether it was clear that these would not be needed for this span.

Hi Guys Reading up on the construction methods of timber suspended floors, there seem to be different views on what span requires sleeper walls. Can anyone tell me whether sleeper walls will be necessary for joist spanning a 3m rear extension, so I guess the timbers would be 2.7m? I...

Thanks guys, I phoned the number on the brochure, which no I never read :oops: and they confirmed what Woody said about not needing build over permission as the sewers are not being shared. Saves me some money. This and the discovery yesterday that the existing bit of extension that I need to...

Hi Guys, I was under the assumption that as I have sewer pipes at the back of my house and under where the extension will be built, that I would need Thames Water build over permission. A colleague at work, who is familiar with domestic building practices for insurance purposes, said that...

Great - sounds like that's goign to be a whole lot easier to remove than deep trench fill foundations..

Woody, Thanks for the quick response. Could you explain that a bit more please for my own benefit please. Is this likely to be a reinforced slab where the load is spread everywhere rather than onto a foundation. I did knock through the airbrick cover to take a look internally and it looks...

Morning Guys, I've recently posted a couple of questions on the subject, but I'm about to start a rear extension and am having the plans drawn up as we speak. As half of what will be the extension is currently a 1960's single and flat roof extension, I thought I'd dig an inspection pit on...

These are photos of the inspection pits I dug on the existing extension. Very shallow

Hi Guys, Thanks for the posts. I must say, I thought the suspended timber floor would be cheaper than the concrete slab, but appears I'm wrong. We actually have an existing half of the extension (which I will need to demolish), with it's own slab about 30cm above ground level and the other...

Sorry moderator and anyone else I confused. Had just been viewing another thread in 'Electrics' and simply posted. Was meant to be in the Building forum.