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Underfloor insulation saga
My underfloor insulation saga, and understanding of damp issues goes on and on.
I’m a few streets away from the area in South Manchester with severe flood warnings. After 3 inches of rain in 24 hours I was more relieved than worried to see a puddle under the floor in the bay and across the front part of the house, because I believe it confirms that the water table is higher at the front of the house than the back.
This is despite the ground level sloping down from front to back of house. The puddle disappeared within 24 hours, and it’s back to its usual dank state. I think the big trees to the back of the house are probably keeping the water table lower there because I have never seen puddles in the back garden in the 30+ years I’ve lived here.
In early November I had 6 old clay bricks replaced with new higher flow ones at front and along one side. Timbers along the front were also treated for some signs of woodworm and currently inactive dry rot. But I still haven’t acted on recommendation to lift paving at front and sides of house to reduce external ground and provide better drainage, as I wasn’t sure how effective that would be.
My instinct is that suspended floor is still looking too risky due to the high water table and in fact since November we have been considering converting the suspended floor into a solid floor, filling in the <1m void below the original house with blown in Leca, topped with Leca screed. However we will probably need a different solution for the shallower void in rear extensions because it looks as if the Leca material won’t provide a good enough u-value in that situation.
Questions
– does anyone have experience of ground floor insulation where there is a high water table?
– does anyone have experience of converting suspended floor to solid floor (of any kind) without replacing all the pipework currently running between and under joists? It sounds tricky…
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9 Replies
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Be very careful if you go to a solid floor – you may well give yourself more problems with damp rising up the walls. How old is your house? You might want to look at the Traditional and Listed Building Advice – there is very good advice given there about reducing ground levels and the problems incurred by putting in solid floors.
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Ps, my instinct is that by lowering your ground levels you may well see a substantial decrease in the amount of everything horrendous! Do you have any pictures of your ground levels?
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Agree with the posts above, and wanted to add the groups suggest if you are going to have a solid floor, hempcrete with a foamed glass filled gap around the walls will minimise the risk of driving damp into the walls.
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As a first port I would lift the flags. Look at the possibility of installing a French drain.
My husband grew up in the Heatons, said their 1930s semi that had a void under the hallway, behind front door, used to fill a bit with water in very bad weather. There was originally a stream on his street, in fact it’s still visible in spots.
So take heart, that house is still happily standing! I would look at filling the void as a very last resort after exhausting all other options. Other suggestions here are good, also try the SPAB for advice on old homes, they have a helpline.
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Also, I’ve seen air bricks shaped like a periscope. The outside grille brick is higher that the inside vent, with a bent tube linking them.
They are used when the outside ground level is too high/has been raised higher than is should be, so let air down into the subfloor but doesn’t let the outside rainwater water in. It doesn’t solve the problem of a higher water table, but may buy you some ventilation. The subfloor must be ventilated, you can’t make it airtight, it will rot!
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Eearly last November five traditional air bricks replaced with new hi flo vents. There appeared to be a significant decrease in humidity in the crawl space at that time, but don’t have enough historic data to compare against external humidity and temperatures. And not much sign of timber moisture readings falling. All very confusing
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It is confusing, you have to become a detectorist in your own home. Problem is there’s no one size fits all approach! Shame about your joists running the wrong way too. Good luck with it. I really think with these problems it’s lots of small improvements that will overall tip the balance in your favour of a dry, ventilated house.
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Unfortunately it’s already been a year since I was expecting to have the ground floor insulated and draught free, and ground floor has been pretty much out of use since June, so time is the one thing I don’t have. And when each small improvement is costing me about £1k a time, I can’t carry on much longer
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Glad I’ve read this. I’m just about to do the same project. I’ll be making sure the floor is properly lined with DPM to stop future damp.
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