It's an old post but in case anyone else finds themselves here in search of advice...
As some other replies have said & as the original poster finally did do,
K18 mechanically fixed is what you should do with solid walls. K17 or any other boards on dot & dab adhesive on exterior walls can detach if damp gets into adhesive. Not much fun. Kingspan's advice is on their website for a reason! Dot & dab is appropriate for cavity walls.
Cement render alone does not totally protect against damp. It develops tiny hairline cracks which water gets thru' - one the reasons for it blowing. Breathable exterior paint eg sandtex etc - must be well applied & maintained to resist water getting thru' it & your solid walls. Natural lime render is different as it is reputedly self repairing.
With solid walls make sure your pointing is in good condition. Usually it will (and should) be natural lime mortar in solid walls, particularly stone walls - this helps control any damp in the brick / stonework.
If your planning dept are amenable & your property is suitable, exterior insulation & render is a good solution (no loss of internal space) but creates a set of it's own issues. Just because other houses don't have it doesn't mean you can't. It is still a fairly new idea that not many have done yet but the numbers are increasing & planners more aware / understanding. 30's rendered semi's are ideal. If you live in a conservation area or a lovely georgian brick terrace then the planning dept will have something to say! (internal only for you)
The thickness of board you may need is related to the thermal loss calculations required in fully spec'ed building /renovations. Depends on several interrelated things; wall construction, floor construction, type & area of windows, roof construction if single storey etc. There are statutory minimum U values to achieve (in the ideal world!). With solid walls you may be looking at circa 75mm but don't take my word for it. There are websites with useful advice. Obviously expanded polystyrene is a lot cheaper but less effective than phenolic board. The phenolic will give you the same effect but with less thickness.
If you have suspended timber floors they can be insulated between the joists if you have to replace boards as part of your renovations or can get to them from below.
If a job's worth doing it's worth doing well - this is a long life project -you will not want to be doing it again in 10 years time or kicking yourself for being a cheapskate. Heating costs have gone up by 63% in the last few years & are never going to get cheaper. Good insulation is the best thing you can do....
Hacking the plaster off (which IME in 1930's & earlier houses is often poor condition) is a very dusty, messy, tedious job. It does give you the benefit of gaining 10-20mm in room space per wall, maybe useful as you will be losing a lot with boarding. The walls are not guaranteed to be dead flat with or without plaster! You will have to adjust your battens to level as much as possible. Plastic spacers...
The point of the battens is to keep the boards off the outside walls. There is a v small benefit of the air gap in insulation.
Use Metal C studs if galvanised or Tanalith (pressure treated) timber battens but not untreated timber! Self treated timber will not be long lasting enough. I am actually suspicious of timber or metal in these potentially damp spaces but there aren't really any other options easily available. I have used once, thick plastic strips fixed with stainless screws but it was a pain. Probably still be there in 100 years time tho. No DPM / DPC required. You would have to screw through it anyway.
Battens for kitchen units are an awkward necessity in dry lining. Planning your exact wall cupboard height in advance is tricky. Also spoils your nice insulated shell. You can set them to be level with the back of the plasterboard surface, mark their locations on the face (& in your notebook)
Some detailed attention is required when butting boards together in corners - rebate / cut plaster back on one board etc. The point being to get a solid run of insulation without breaks in it. Also round window reveals - there are thinner boards available for this. Of course if you later replace your windows then this can be altered / improved to better specs. as can the window sizes (smaller to allow more insulation / less cold bridging)
Many boiler installs are done in porches / lean-to's / basements - against solid walls. Plumbers don't seem to be bothered... The 5 year old boiler that came off our basement wall was very rusty... Nothing to stop you mounting it on your dry-lining but must be v solidly fitted - boilers are heavy - full of water. Check out boiler maker websites for fitting advice.
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