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Adventures in the subfloor void (insulation etc)



Have pondered going into the tiny crawl space under the ground floor (timber joist subfloor) for a few years, but general claustrophobia / fear of spiders and dark places have hampered my motivation. Anyway, last months bill from Octopus Energy has given me all the impetus I needed, and I've embarked on a bit of a project.

Dropping down through the tiny hole in the hall (cut from 4 small floorboards), I did my best Harry Houdini and maneuvered into a horizontal position. A couple of halogen lights have made the space more welcoming and I've gone on a potholing adventure...

Basically there is almost NO insulation down there. I wasn't expecting any in the floor, but even the pipes are bare, and the central heating system is only 10-12 years old (previous owner installed). I recently upgraded the subfloor vents to the modern plastic ones and its blowing a gale down there; little wonder the bills are so much...

Have worked on it for several weekends now - the time taken to get into position and general discomfort means the work is very inefficient and only a few pipes will get done in an afternoon. Come up caked in dirt and dust.

T-junctions have been treated with Spiral Wrap from Screwfix, secured with aluminium foil tape

All foam sleeves have been secured with at least two zip ties (read the heat can make the curl off)

Have now bought several rolls of Knauf insulation to fit between the 125mm joists, supported by netting stapled to the joists. Hoping after I've measured and cut outside, the hardest part will be getting the insulation to the work face... Building Control have advised a vapour control layer shouldn't be necessary - I'll go down a couple of times over the next few years and inspect for damp / condensation etc

Some real shoddy work down there... pipes supported by old zip ties, drainage from the kitchen not laid to proper falls etc

Also, worryingly, the mains water pipe is lead for at least 6m before it connects to the new push fit plastic pipe. Does anyone have any experience of changing lead pipes, cost etc? Is it THAT much of a problem being such a short run?

Wish I'd done this years ago now...



Edited by Rowley
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Mirror Mirror

Interesting reading. Made me think of the secret tunnel at Colditz, which after descending from the clock tower, was constructed under the chapel floor, similar to you, in the crawl space between rock and floorboards.

In their case, the builders of the tunnel had to cut through 12” square oak beams with saws made from cut up tin cans.

Regarding your lead pipe question, I’ve no corroborating evidence, but I think as long as it’s not disturbed, the inside of the pipe will have a crust on it which largely separates the water from the actual lead of the pipe. If you’re really bothered, you could run the taps for 2 minutes each morning before drawing water for consumption, but I appreciate this has a cost, if you have a water meter.

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Agree with Mirror Mirror. The lead pipes will have a coating of limescale so there should be no issue. Regardless, I always flush the bog first thing before drawing any drinking water. Generally, the pipes will be lead all the way to the water main so likely much more than 6M.

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