DIY external insulation on a single wall.

[justsomeguy]

Over the weekend i was drilling a nice 110mm hole for the extractor of our rearranged room. turns out that a whole side on the extension is medium dense block... with no cavity.(just external render (a very strong mix)) I know that the back wall has a cavity as i had the patio doors replaced and could see it. don't hold much hope that the flat roof has anything in it insulation-wise at all..

It's only a single floor extension built in the mid 80's and that 10 meter wall has only a single small window, I have about 60m2 of 25mm XPS in the shed, from when i did the floors (had some odd deal on where 3 palettes cost £10 more than 1) so i was thinking just put some 25mm battens put one layer between them and one or two layers over, then more battens and shiplap on the outside. as the xps is water repellent it shouldn't need a membrane  should it?

Dave

[dhaslam]

There isn't much that you could do to a solid wall that would do it any harm.     It is  just astonishing that a wall could be built like that in the '80s and even more amazing if the roof is not insulated.    It might be advisable to increase the wall insulation above 50mm if the room is regularly used and heated.     

[Hugo]

Just over a year ago I was drilling a hole in my bedroom wall to put in a 13 Amp socket and the drill bit went into the garage.
It turns out that almost the whole length of the garage internal wall is single brick, that's Two bedrooms worth, also no insulation in the garage roof, there is now mind you.
I was thinking on the same lines as you, batten and insulate, then over board with plaster  board.
The only reason that I haven't done it yet is because the mains electric cable runs up this wall into the consumer unit.

[justsomeguy]

There isn't much that you could do to a solid wall that would do it any harm.     It is  just astonishing that a wall could be built like that in the '80s and even more amazing if the roof is not insulated.    It might be advisable to increase the wall insulation above 50mm if the room is regularly used and heated.     

It gets worse the things i've bumped into... fuse box wired so badly no actual fuses (all wires went into the busbar.) some sockets done in 5 amp flex, outside 2 pin plug (not socket) hanging on wall...LIVE, sparky said that he has seen all the faults before in the 30 years he's been a sparky, but never in one house...

Heating needs a bit of rework as the 22mm pipe from boiler goes 2 feet (behind wall) )then whole house (30,000BTUs) in 15mm  (this has taken 12 call outs on the boiler insurance to work out why it keeps breaking down (every part of boiler apart from case has been replaced at least once)

So no insulation...not surprised any-more...