Help Single Skinned Extension

Discussion in 'Builders' Talk' started by WDWGunner25, Feb 25, 2020.

  1. WDWGunner25

    WDWGunner25 Member

    Hi all,
    Really looking for some advice and freaked out we have made a gigantic mistake.

    We completed on our first home today and as we were moving in I noticed that there was some damp on the extension wall that I didn’t see mentioned on the survey (we paid for the best survey available). I’ve since gone back and re read it this evening, and I feel like a complete idiot as I missed the fact that extension is single skinned!!!

    Now It is just a garage, utility room, downstairs shower room and a small room called the ‘garden room’ nothing like a kitchen or bedroom, and our surveyor did not mention it as an issue on the survey (on a scale of 1-3, 1 being no problem to 3 urgent it was rated a 1) but did say about adding cavity insulation in future as some damp and condensation is to be expected.

    I believe it was built like as they didn’t get permissions (it’s 18 years old) and we have indemnity insurance in place because of it. BUT im now completely panicking that we’ve made the rookiest of errors and will be saddled with an unsellable money pit.

    Does anyone have a ball park for how much it would cost to fix and if it’s worth it? The rooms will be storage mostly other than the shower room. I was gonna have a little bar in the garden room but I’m unsure now.

    Any help massively appreciated!
     
  2. Severntrent

    Severntrent Screwfix Select

    When you say single skinned do you mean 1/2 brick thick (102.5mm) or 1 brick thick (225mm)
     
  3. Astramax

    Astramax Screwfix Select

    Don't over worry, I have a single skin conservatory, I applied 2 coats of Synthaprufe to the walls, fitted 2" x 1" treated battens @ 16" centres and put 1" polystyrene insulation in between, overboarded with plasterboard and skimmed it ..........that was 30 years ago, dry as a whistle inside and never had a problem
     
  4. WDWGunner25

    WDWGunner25 Member

    It’s a ‘solid 110mm brick wall’
     
  5. WDWGunner25

    WDWGunner25 Member

    If it helps this is what the survey said:

    The single skin garden room and utility walls will inevitably allow some penetrating dampness. Internally these walls have been plasterboard dry lined. The vendor advised insulation is incorporated behind the plasterboard. Although this will prevent most moisture penetrating across and causing decorative deterioration the moisture penetration will in the longer term cause deterioration behind the plasterboard and insulation. In the longer term replacement dry lining will be required.
    It must be accepted that a solid 110mm brick wall will allow some penetrating dampness and unless this part of the building is upgraded to cavity construction future maintenance will be greater.
     
  6. Astramax

    Astramax Screwfix Select

    Are you sure it's damp and not just condensation as you say a utility room so may have had an appliance stood up against it simply reducing air flow.:)
     
  7. Astramax

    Astramax Screwfix Select

    Surveyors will cover themselves, don't over worry it's a trivial matter and easily remedied.
     
  8. WDWGunner25

    WDWGunner25 Member

    That’s a picture - the external wall is directly on the outside of that area, we knew we would have to get a down pipe sorted there simply because the rain water runs down it, but our survey said there was currently no evidence of damn internally. I admit I’m a complete idiot with this stuff but that looks like mould etc
     

    Attached Files:

  9. Astramax

    Astramax Screwfix Select

    The down pipe issue may well be the cause of the problem, the mould on the wall can be removed using household bleach applied over it and washed off after leaving it to soak for an hour.
     
  10. WDWGunner25

    WDWGunner25 Member

    Thanks Astramax, it’s been quite a day, I am a terrible anxiety sufferer and I have flu during the move so it’s all been brewing, but what you’ve said is comforting. In your experience is adding cavity wall insulation expensive? Just as a project for the future!
     
  11. Astramax

    Astramax Screwfix Select

    Cost will not break the bank, various types of insulation available at varying cost starting from a few pounds depending on what insulation you want to suit your requirements as mentioned earlier the 1" polystyrene would probably be inexpensive but effective to a higher spec such as Kingspan or Cellotex insulation products.
     
  12. rogerk101

    rogerk101 Screwfix Select

    I have just finished adding EXTERNAL insulation to the outside of my single skin brick wall garage. I covered the whole of the outside of the building with 100mm boards of rigid insulation fitted snugly between vertically mounted 100 x 47 timbers, which I attached to the brick wall. This was followed by the next layer of 100mm boards of rigid insulation fitted snugly between horizontally mounted 100 x 47 timbers, which I attached to the vertically mounted timbers. Outside that, I added vertically mounted 25 x 38 tiling battens to provide an air ventilation space behind the final cover, which is 225 wide feather edge timber cladding. The whole effect looks fantastic, didn't waste any internal space, and is far, far more thermally efficient than any internal insulation would ever provide. I did it all myself and didn't pay much more than £5000 for materials.
     
  13. WDWGunner25

    WDWGunner25 Member

    Thanks Roger - we wouldn’t be able to do it ourselves (wouldn’t know where to start) but good to know it won’t run into £10,000s.

    I think we are gonna get some quotes but for the most part just leave it for now and make sure it’s well ventilated until we tackle the other jobs we saved for like some work to gutters and doors
     
  14. rogerk101

    rogerk101 Screwfix Select

    I should have mentioned that my garage is 2.6m high, 4m wide and 6.5m deep, so that should give you some idea on what your materials might cost.
    The main point that I was trying to stress is that if it's at all possible to insulate it externally, you should do so. It's much, much better than internal insulation which is riddled with all sorts of issues, like thermal bridging, condensation, not being able to hang heavy things off wall, etc.
     
  15. Mr A greig

    Mr A greig Member

    If it gets to the point it's too far gone it won't be an obscene amount to pull off plaster install damp proofing of some sort and insulate.
    I belive XPS polystyrene works best where damp is an issue.
    In the mean time a decent dehumidifier will go a long way to reducing the problem. Compressor dehumidifier is better for warm areas and electric desiccant is better for cold. Cheap peltier ones are a waste of time.
    I would however address the downpipe as a matter of urgency.
     
  16. WDWGunner25

    WDWGunner25 Member

    That’s really useful! And YEP! We’ve already emailed a few people of check a trade for quotes on the down pipe - we always knew that would be a major priority
     
  17. Rad87

    Rad87 Member

    As others said, don't worry... at least try to :) I am actually considering building a single skin porch now. I am actually surprised that people try do to stuff like rogerk101. So you added 260mm to the walls on the outside? Did you change the roof overhang? That seems to be a lot of work. And timber underneath feather edge may still get wet.

    Why not use grey Styrofoam with PU + mechanical fixing and render on the top?
     
  18. Mr A greig

    Mr A greig Member

    I spent 100 quid on a dehumidifier a couple years ago and it's had paid for itself many times over with the damage that's been avoided with the various 'incidents' that i have had.
    Single skin brick construction isn't the end of the world, most new houses in Scotland are timber framed with single layer of brick.
    Cavity insulation would be cheapest but if the plaster is already damaged you would be aswell spending the extra to remove and do it right.
     
  19. rogerk101

    rogerk101 Screwfix Select

    Actually the reason my whole garage to granny flat conversion came into existence was because the previous roof had rotted away and needed to be replaced. I wanted to make more use of the roof space under the new roof, so widening the whole building by over half a metre, and changing the roof from single- to double-pitch gave me very nice useable space upstairs. I have soffits that add another 260mm on each side, so even in the recent wet windy storms, the walls under the soffits stayed dry. The feather edge overlaps by 50mm, which leaves 175mm exposed. Good luck on any water getting behind that, but even if it does, there is a 25mm air gap with vents below at ground level and vents above at soffit level, so the planks will be dry within a couple of days max. Would can get wet without any problems. The only time problems occur is if it stays wet.
     
    Rad87 likes this.

Share This Page