Redbeard

I cannot find it immediately in Part L but how about this which shows the method and refers specifically to Part L: https://www.hertfordshirebc.co.uk/guidance-note/designing-domestic-extensions-guide-to-compliance/ ?

I suggest you put your values into something like this https://www.calculator.net/right-triangle-calculator.html?av=&alphav=17&alphaunit=d&bv=3400&betav=&betaunit=d&cv=&hv=&areav=&perimeterv=&x=Calculate and ask how he gets something different. Or buy him one of these (I have no connection with this supplier) https://www.ebay.co.uk/itm/286798055236?campid=5338947458&mkevt=1&mkcid=1&toolid=10050&customid=&mkrid=710-53481-19255-0&loc_physical_ms=41684&loc_interest_ms=&campid=5338947458&mkevt=1&mkcid=1&toolid=10050&customid=519bad6e777c152ae5f5c591c56048c7&mkrid=710-53481-19255-0&loc_physical_ms=41684&loc_interest_ms=&msclkid=519bad6e777c152ae5f5c591c56048c7 and then get him to tell you where the wall-plate has to go. It's worth noting that if your tiles are for min 17 deg pitch then a bit more gives you 'weasel room'.

And the gutters are on the end of the oversailing spars? A lot of stress on that joint, I'd guess. How many rafters? 1st thought was steel plates, but that's a lot of fabricating, particularly if you do them both sides.

My last IWI stint was just into the new 'regime'. I was client, PD and PC. It was well within my sphere of experience, but it has made me think re more 'complicated' jobs. Not so much will I need dwgs, but will I be able to 'prove' the 'skills and competencies' (or whatever the wording is) to the 'powers that be'. I have no doubt that I have them (all this is stuff I have done many times for myself and others), but will 'the system' be satisfied?

Only if you say it more than once.

It could work, but I have to say I have never heard of cheek ventilators. Might you perhaps be asking a lot of the air to follow a tortuous route? (I don't know the answer!). I do like the idea of a builder even thinking of venting the cheeks, though. I am not sure I have ever come across it before.

My contractor used mainly 40+mm limestone, with no fines. I don't think there were any stones under 30mm. but what you show looks fine, and fines-free. Really as long as it lacks fines which could emulate cement you are probably OK.

Yes. As the existing plaster will be an unknown quantity in a 1950's house (?breathable?) you may be best to hack that off and do a 12mm lime parge coat. Tooth it for about half its thickness and bed the boards in, then mechanically fix with plastic hammer fixings. Finish with a toothed coat of lime plaster, then mesh, then another coat, and just trowel up if you like a coarse finish, or use a fine lime finish if you like 'mirror-polished'. @Roger440 said "WUFI assesment is an awful lot of money to do just a wall or one room though." Yes, agreed, and practitioners sometimes hard to find, too, but not if the OP is maybe going to add IWI throughout the house, and also not if your WF merchant offers the service for free, as at least one does.

Absolutely fine to add insulation, but your initial post suggested that he saw the removal of the plaster as a 'trigger' point *requiring* you to comply with Part L (which in this case I am pretty sure it isn't, as the wall already complies). You could do just PIR, or you could consider an insulating plaster, or wood-fibre, or whatever you are comfortable with. I like wood fibre a lot. Whatever you decide to do it's worth getting a WUFI dynamic condensation risk assessment done.

I do not (and as I read it the Approved Document L does not) agree with your BCO. Page 26 of Approved Doc L has a table (4.3) showing a threshold U value (0.7) and an improved U value for filled cavity walls. I am pretty sure that UF foam (if still intact as you suggest) would give you 0.55W/m2K in a 65mm cavity, if rockwool is reckoned to do in a 50mm cavity. Anyway, as far as I am aware (although it is often misinterpreted) the 0.7 threshold means that if it is worse than 0.7 you have to achieve the target (of 0.55). I am even more sure it will have achieved 0.7. It sounds like your BCO is trying to make the 0.3 target for solid walls stick. I would write to them saying your wall already complies and that, accordingly, you will be taking no further action. Edit: Seen a lambda figure of 0.029W/mK for UF foam. At 65mm, with a base-case R value for the original unfilled wall of around 0.66m2K/W, that should give you a U value of around 0.35W/m2K, WAY better than table 4.3 requires a cavity wall to achieve.

I have used 21 Degrees (formerly Green Building Store). 21 Degrees seems to be a big network, so it's their Huddersfield office you are looking for - Chris Herring and Bill Butcher have been my contact-people.

When you say the soakaway is > 5m from your boundary I think you mean the front one. Having seen your latest pic I'd guess your house to be about 5-5.5m wide (?) and I believe the required distance from boundaries to be 2.5m minimum, so depending on the surface area of the soakaway, if my estimate is anywhere near right, you could be close to the limit side-to-side. In any case I doubt anyone is going to quibble unless your neighbour objected anyway. You say: But if you used my 'grating' idea you could keep the level well below the DPC, keep the aco drain at the bottom of the 'trench' and still lead any water away to the soakaway.

Thanks! Good! Not least as it suggests the contractor is on the ball re guidance - except perhaps for the level at the house. It's difficult, isn't it? We all know BC recommend 150mm below DPC, and ditto that no-one told the rain in many areas that it should only splash up 150. But we also know we need not to fall into a trench as we open our front door! If it were me and I wasn't ever intending to wear stilettos (and nor were any of my potential visitors) I think I would do the drain much lower, with a 'boot-scraper'-type grating over the top at the desired 'pedestrian level'.

5m from my boundary And at least the same from any buildings (incl your own)?

How far is the soakaway from the boundary, and from your building and any neighbouring buildings?

AFAIK Type 1 'MOT' has lots of fines in and can almost set like concrete. It is not what you want for a permeable base. My contractors used 300-500 40mm limestone with a permeable membrane over, then 'permeable block paviours' (which have an extra gap formed by nobs on the sides) with large (3mm-sh) grit in the resultant gaps. It performs excellently, although the natural ground below the limestone is clay and bedrock. If I sling a bucket of water onto the paving it just goes *slurp* and it has gone. Try putting "can MOT type 1 form a permeable base?" into a search engine, though, and you will get the whole spectrum, from yes, very much so to 'no, it is impermeable'. My experience suggests that the latter is the safest one to believe. Others' experience might be different... And as for the advice re a French drain, 'to direct the water away from the house wall', it has to have a destination. What is it? Is it a soakaway? If so is it the requisite distance from buildings and boundaries?

I wouldn't put any concrete against the wall. It gives you a joint which will crack and open and let moisture in. Membrane and gravel and, if you have somewhere for the water to drain to, perforated pipe in the bottom of the trench - although it doesn't really seem deep enough to count as a trench, or perhaps the pic is misleading. How deep is it?

But no point. The joists themselves are the thermal weakness. Agree if you just 'posted' deeper WF to hang below the joists, leaving the joist bottoms 'naked', but my hope is that there is sufficient crawl space for a cross-layer of rigid WF underneath (or flexi WF in a form of 'Larsen Truss' (spaced joist, @ChurchAl, if you haven't come across the term before)). That way the thermal bridge is mitigated.

Is it single-storey?

Agreed. How much clearance/crawl-space do you have below the joists? If you can 'underdraw' with further insulation then you can also 'cloak' the thermal bridge of the joists. I'd go for as close to 300 as you can. Although the temp differential between room temp and 'outside' (under-floor) may be only 21 or so at 0 degrees external, the temp diff between the flow and the ext temp will likely be a minimum of 40.

Sorry I am the first to chime in. I think you need a Structural Engineer and an 'invasive survey' (expose enough of the lintel to see exactly what it is so the SE can calculate - not guess.) My (definitely non-SE) feeling would be that whatever dead load that lintel is designed for it was not designed for the live load you refer to.

It is hard to tell, but the base coat looks much too rough in parts for a 1.5 'gritty-coat' to 'hide'. The 'tramlines' simply should not be there. A little off-flat, maybe; tramlines, no. They should have been sponged out when the render was stiff but still 'moveable'. Of course we have not seen the whole surface but (assuming everything is now hard as a hard thing) the 'tramline bit' needs another coat, in my view.

Is there a nuance here in relation to the 'after completion PD'? @kandgmitchell rightly point out that your 'during works' use seems to be covered 'for the duration of operations ...' . Then it becomes 'un-PD', but would be PD after completion if you erected it again! If the Planners notice I wonder if they could require you to take it down in order to re-erect it?

I m a little confused by the first few posts. Isn't the easiest way (to find out whether the potential extra space exists) to take off the architraves and measure the masonry opening? If you want to be truly 'belt-and-braces' you could hack a little plaster off on both sides above the door to see by how much the lintel bears on the masonry each side. This would give you an idea of whether, in extremis, you could widen out the masonry opening without risk - a not inconsiderable task, BTW. Find the dimensions of your composite door *and frame* and if that dim is smaller than the masonry opening you are set to go. If not, you're not.

I think moss gets so much less of a 'key' on clay than concrete, particularly when the concrete is deteriorating. I wonder if you will have an issue at all.