Damp in an old house is almost never one problem. Roger Bisby walks through a 1900s renovation near Nottingham to work out where it is really coming from.
The short answer is that most of the moisture here is coming up from the ground rather than in through the walls. There is no damp-proof membrane under the floors, the clay subsoil is holding water even after weeks of heat, and hard sand and cement render is trapping whatever does get in. The cure is ventilation, a proper membrane lapped up the wall, and belt-and-braces damp-proofing rather than tearing out a damp-proof course that is still doing its job.
AJ went to auction on this place, watched it fail to sell, and bought a house that had stood empty for years. He is turning it into a multigenerational home for himself, his wife and his parents, with the old garage block becoming a self-contained side for mum and dad. Stripping out the ground floor turned up rotten skirtings, crumbling fireplace surrounds and a mystery black coating on one of the floors that turns out to be a piece of local building history.
MENTIONED IN THIS EPISODE 👇
Dryrod DPC Damp Proofing Rods
https://go.skill-builder.uk/dryrods
Drybase TS-PLUS Tanking Slurry Kit
https://go.skill-builder.uk/drybase-ts-plus-kit
Drybase Flex Membrane
https://go.skill-builder.uk/flex-membrane
(Above are affiliate links. We earn a small commission at no extra cost to you.)
AJ on Instagram 👇
https://www.instagram.com/the.multigeno.reno
KEY TAKEAWAYS
• Dry rot draws moisture in from elsewhere with its roots, so cutting out the localised damage is not enough, whereas wet rot dies once you take the water away.
• If a house has an original slate or bitumen damp proof course, leave it alone. Drilling into it destroys it, so go above it or below it if you want to add chemical rods.
• Air bricks at the front only give you ventilation at the front. Without a matching route out the back you get no through flow under a suspended floor, and moisture just sits there.
• Clay subsoil holds water all year, which is why a floor with no damp proof membrane can still be visibly wet after a long dry spell.
• Strong sand and cement render with waterproofer in it does not solve damp, it just moves the problem into the wall and pushes the moisture somewhere else.
• Coal tar was used extensively as a damp-proof course and membrane material, and near an old colliery it is exactly what local builders would have had to hand.
• If you are fitting retrofit underfloor heating, get the drawings from the manufacturer and follow them to the letter. Ignoring them is where these jobs go wrong.
WATCH NEXT
CHAPTERS
00:00 A 1900s house being turned into a multigenerational home
00:45 Dry rot or wet rot, and how to tell the difference
01:09 Suspended floor, solid floor and missing air bricks
01:40 The survey findings and no DPM under the fireplaces
01:56 Retrofit underfloor heating: gas now, heat pump later
02:45 The original damp proof course and why you must not drill it
03:20 How chemical damp rods actually work
03:57 Internal wall insulation on the external walls
04:43 Digging out the floor: clay, tiles and no membrane
05:24 Building a new slab the right way
05:55 Boiler position and following the underfloor heating drawings
06:39 1980s inset fireplaces and where the chimney damp comes in
07:13 Wood burners and a lifetime supply of wood
07:37 Three phase supply, EV charging and a future heat pump
08:14 Rotten skirtings: wet rot and woodworm
08:47 A quick word about the statue
09:41 Auction, trees and the condition it was bought in
09:59 The mystery black coating on the floor
10:53 Sealing the floor and lapping it up the wall
11:41 Hard sand and cement over an old damp problem
13:25 Wrapped joists and moisture under the newer floor
14:11 Cutting a channel through for ventilation
15:38 The tar smell and what it tells us
16:44 Coal tar as a damp proof course
17:55 Converting the garages for the parents
18:33 The gardens, palm trees and fruit trees
20:01 Follow the renovation on Instagram [HANDLE NEEDED]
Renovating something similar? Tell us what you found under your floors in the comments.
#damp #renovation #oldhouse #SkillBuilder
