Worried that extension has not been built to building regs

Discussion in 'Builders' Talk' started by t1redmonkey, Jan 28, 2021.

  1. t1redmonkey

    t1redmonkey Member

    Well he asked about it, but my builder said he had photos of it going in and an email from the structural engineer giving the calculations (which he didn't actually show to the guy from BC, but he said it was fine if he emailed it on to him later so hopefully he actually does have that). To be fair I wasn't that worried about the RSJ because I do remember the structural engineer coming here before work started for that specific reason, and they showed me it after they had 'installed' it and it looked like that was properly done.
     
  2. Mr Rusty

    Mr Rusty Screwfix Select

    Well, like others, I am surprised, but there you go - good news and hassle avoided. I am most surprised that an extension, which will be exposed to the house heating system, has been allowed to be rebuilt as single skin, but I guess it is borderline a "repair" as you have re-used existing footings. If BC are willing to sign-off then that's good enough.

    A couple of further points. The walls, if uninsulated single skin, will be cold, and will be prone to condensation. If you have the space you could consider building an insulated inner "wall" and creating a ventilated gap between the single skin and an inner stud wall. i.e. reproduce the structure of timber frame where the insulated frame has a separate brick skin separated by a ventilated cavity, but in this case your stud wall would be non-structural. It will be humungously warmer, for the cost of ~ 150mm. You now also know the correct procedure for future work. :)
     
    Joshuaojs likes this.
  3. t1redmonkey

    t1redmonkey Member

    Yeah to be honest I was hoping BC were going to ask the builders to redo the walls in the way you described so I wouldn't have to get that done additionally in the future. I had the same problem with condensation in that room previously since it used to be a bathroom, so you can imagine the combination of a bathroom + single skin walls was not good. At least now it's not a bathroom but yes probably going to have those same problems eventually unless I get that improvement you mentioned done.
     
  4. Severntrent

    Severntrent Screwfix Select

    Are we talking single skin or 1 brick thick, there is a subtle difference
     
  5. t1redmonkey

    t1redmonkey Member

    What's the difference between the two?
     
  6. Kas228

    Kas228 Screwfix Select

    Spot on advice, I assumed he would be doing this as a matter of course otherwise it will be freezing and a massive energy loss point....
     
  7. Severntrent

    Severntrent Screwfix Select

    A skin is half brick thick 102.5mm i.e. laid in stretcher bond. 1 brick thick is full brick 215mm, flemish bond, English bond
     
  8. t1redmonkey

    t1redmonkey Member

    On original survey for my house, it said the extension was 'single skin brickwork dry lined internally'. Not 100% sure what it is now, but I think it's basically the same since they have just built on top of what was there? Maybe slightly thicker. I may contact the BC guy later to get clarification on what it is now called.
     
  9. JasonCSmith

    JasonCSmith Member

    Something doesn't add up here. Redmonkey mentioned his builder has said he used 'dense concrete blocks which is better than cavity insulation'. Looking at the photos he has provided it looks like there's an 80mm internal reveal, and about a 75mm deep external reveal. Add those dims to a nominal 65mm window frame and you're at around 220mm overall thickness of wall (excluding the render parge coat). Take say 25mm dot & dab off that and it leaves you 195mm thickness of wall. So has it been built in 190 dense block built off an existing 9" brick base? Or maybe 2 skins of 100mm block? Dims don't work out for 103mm brickwork or 215mm brickwork. And I still seriously doubt any BCO would be approving of an uninsulated half brick thick wall.
     
  10. Severntrent

    Severntrent Screwfix Select

    May just be a term thing
     
  11. t1redmonkey

    t1redmonkey Member

    See the thing I am a bit confused about is I don't think it's the same thickness all around the perimeter of the extension. I think that on the side with the door, it is thicker than it is on the sides. I mean this might be me being really sceptical, but I think what might have happened is they used 2 different thickness of blocks. They used the thick ones around the door part, and then thinner ones around most of the rest of it. I took a measurement of a block beneath the door for example, and that is very thick, but the rest of the extension is 100% not that thickness throughout.
     

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  12. JasonCSmith

    JasonCSmith Member

    Stick you head out of the side window and measure the overall thickness of the wall. Take a total of 25mm off for the plasterboard & adhesive dabs internally, and then about 10mm off for the external render and that'll give you the thickness of the blockwork used on the wall in that location.
     
  13. Mr Rusty

    Mr Rusty Screwfix Select

    I think if BC are going to sign it off, it is what it is. You don't have any come back on the builder if it's compliant, so the only decision left then is whether you add additional insulation internally. Personally, I would, because it really does make a huge difference, but that's your choice.
     
  14. t1redmonkey

    t1redmonkey Member

    Ok this is 103mm half brick on the sides then from what I can tell...does that change things? Should I tell guy from BC in case he missed it or is he probably still gonna have the same opinion?
     

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  15. jonathanc

    jonathanc Guest

    i think the critical thing here is whether the existing walls were retained or whether they were demolished and rebuilt. if the former then from a BC perspective i think it is a retained thermal element and no need to improve it. if the latter then i think it is a new thermal element and it needs to be to current standard @Frutbunn interested in your view on this
     
  16. t1redmonkey

    t1redmonkey Member

    I wonder if they deliberately left the base of the walls as they were then for this exact reason. So they could just do the half brick perimeter without contravening building regs.
     
  17. jonathanc

    jonathanc Guest

    more likely so they could tell BC that they've just rendered up the existing walls
     
  18. stevie22

    stevie22 Screwfix Select

    If you're re-using a thermal element then you have to upgrade it but to a lower standard than new work, eg Garage conversion. I can only assume that BC is viewing it as was habitable before and still is so you're not altering anythng. I'm still surprised by that in truth! I did a job a few years ago where the client wanted to replace a flat roof with a pitched one. BS insisted on full insulation to the walls (we were going to add a bit.

    I have to say your builder has been totally unprofessional in not advising you to insulate since it seems as though he has done your design. Maybe he thought you would decide to add it an he would charge through the nose for an extra? (Spot the cynic).

    I share Rusty's view that it would be the right thing to insulate.
     
  19. JasonCSmith

    JasonCSmith Member

    Ok so that confirms that that wall is built from 100mm masonry. I think I can just see the face of a block in the photo so assume it's 100mm block that's been dot & dabbed internally and rendered externally.
     
  20. JasonCSmith

    JasonCSmith Member

    Your BCO may not have realised that the walls were varying in thickness. He might've just looked at the wall below the door and assumed the thickness was consistent on the other two sides. There are two issues here as far as I can see that you may or may not wish to query with your BCO.

    1) Under the building regulations, is a rendered 100mm block wall sufficient to resist the passage of moisture into the inside? My view is no, it is not.
    2) Under the building regulations, should the walls, these having been substantially rebuilt, have been upgraded in their thermal performance, from the ones that were present before? I suspect yes they should have been.
    3) If the answer to 2 is 'no', then on what basis is this as the building regs suggest that a 'renovated thermal element' must be upgraded thermally unless there are reasonably mitigating factors.
     
    jonathanc likes this.

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