Hi, I'm rebuilding the floor in the dining room - 4.1 x 3.9M. The house is a mid-terrace, build 1900, 260mm solid brick walls. When I took the floor boards up, to my horror I found 2 large (180x65mm) joists sitting directly in the earth foundations, with 12 smaller joists running across them. Presumably never replaced and largely buried by damp soil, the joists were in a pretty bad way and the ventilation throughout woefully bad. I've now removed all timbers and started excavating the floor. Plan to go 3ft down to provide a crawl space and better ventilation. My question is, with the floor now excavated how should I hang the new joists. One of the walls remaining is an external wall, so cutting into the brick and installing the joist in the wall isn't really an option. Can I drill and install joist hangars for the two main joists? Would it be worthwhile and cost effective to installing steel RSJ beams rather than timber joists? Thank you.
You're going to excavate 3' down? Have you considered having a solid floor instead - I suspect less work, less hassle, better insulated, and won't rot... (You'd have to porvide through ventilation to the rest of the house's underfloor, tho', if it originally came this way.)
If your house was built in 1900 and the joists were put in as you describe (with damp soil around them) they almost certainly wouldn't have lasted 115 years. I suspect that at some point they've been replaced, or somehow the soil has built up around the joists. If your considering excavating it to a depth of 3ft, be careful, as you may risk causing problems with the foundations.
Thanks for the input. I have considered the foundations and I'm not concerned. There are parts of the floor that are originally lower than the bits that were mounded up around the joists. So in some parts the relative change in soil depth will be closer to one foot. However I will consult with my builder. As for the solid floor. It crossed my mind but I never gave it much thought. Perhaps this would be a better idea.
I'm pretty sure it would be my preferred option. No rot, no springiness, no draughts, well insulated. If the rest of the house's underfloor gets its ventilation via this room, then ducts should be laid from the existing air bricks to keep the supply going - perhaps with some extras added to be sure to be sure. Ventilation is the main key to keeping things fresh under there.
Digging out 3' of soil is a huge amount. Work out the square yardage and think how you will get it out of the house etc. You could take out just enough to go below the bottom joist. Think about block piers on a concrete plate for your main joists and a single block outer wall for the joists to sit on.
Thanks for the replies. Having done some reading I am erring toward a poured concrete floor with a physical DPM sheet that laps up the wall and behind a kingspan DPM and a full replaster. This would provide better insulation on the solid walls and also deal with the damp in the walls. Having already removed plaster to 1200mm - removal of the rest of the old black plaster seems like an appealing choice. A damp proof company visited today and suggest that this would be an alternative to injecting a DPC into the wall and replastering to a height of 1200mm. Any pitfalls with this option?
I dunno. Certainly having a DPM covering the floor and the walls should seal all the damp out nicely But... what's going to happen to the damp that will keep rising? Will it chust escape out the other side of the walls (are they all 'exterior'?) or will they possibly lead to future probs? I dunno.
Yes I had considered as much. Out of sight, in this case, certainly does NOT amount to out of mind!! I presume the only way to really solve the actual problem is to inject a DPC and install air bricks and the timber floor. However, upon reading, the poured concrete and insulated dry lined walls appeals because of the insulation benefits. More reading I suspect.
I'd still go for the concrete floor - there's no connection between that and rising damp up the walls. So, I'd go for the solid floor chust 'cos I believe it's a better solution (well insulated, of course). Then I would most certainly go for a DPC in the walls, and I guess injected is the only practical way. The floor's DPM would be taken a goodly amount up the wall - I dunno what a recommended amount is, but 2 to 3 feet I'd have thought? For the walls, yep I'd strip all the old plaster off if it's at all dodge. Finally, board with Therm Lam Board to whatever thickness of insulation you can afford space-wise. Bear in mind that even the thinnest - only around 35mm total thickness - will be hugely better than the bare plaster walls you had, and anything more is a bonus but will have progressively less additional effect. Perhaps tank the exposed brick first, I dunno. There are some excellent cement-based slurry products available these days that are very effective and easy to apply - just slap it on. Then board over. Use dot and dab and add a few mechanical fixings on each sheet too so's they don't fall off if there's a fire! (Not really sure if that's essential - I'd be tempted to chust use bonding adhesive so's there's no breach of the tanking.) Job is a jobbie, and it'll transform your room's insulation level. (Don't forget the ventilation to the rest of the house's floor - add them ducts...)
Well, after a couple of weeks off the project due to heavy work demands I've been back on the house project and made a fair amount of progress. This week I had designs on laying hardcore and sand blinding in preparation for a DPM > concrete > insulation > UFH > screed > tiled floor. 35cm approx. total depth. Unfortunately, much to my horror, tonight, whilst excavating the offshot I discovered the brick layer only goes 2 bricks (16cm) below the original floor level for a large part of the room. This is not the case for over half the room, but toward the garden side of the house in the offshot it is. It there any alternatives or do I now have to adopt a suspended floor? Really didn't want to go back to this solution, especially as I planned to install a highly efficient UFH system. Thanks in advance.
"...whilst excavating the offshot I discovered the brick layer only goes 2 bricks (16cm) below the original floor level for a large part of the room. This is not the case for over half the room, but toward the garden side of the house in the offshot it is." I don't understand. But then I'm not a builder...
Essentially having dug down below my original floor, which I have removed, including the joists (which were in poor condition). I've found that there are only 2 house bricks before I meet the soil foundations. If I dig any further I suspect I will undermine my foundations!?
Need some photo's to understand this. What is below the two course of bricks, intrested to know what the footings are, if any. Can you not dig a small square inspection hole the width of a garden spade to get some idea.
If that part of the house was built in the 1900s then I suspect that there are no foundations, though I would have expected the brickwork to have been wider at the bottom to spread the weight, sometimes there were oak beams laid first as a foundation then the brickwork.
The house was all built in 1900. I was very surprised to find such a small amount of brick layers below the floor. I've basically reached the footings. Do I correctly presume that digging down past the last layer of bricks into the footings at 16cm deep down another 15cm is a no go? Plan was: Hardcore 10cm Sand 4cm DPM Concrete 5cm Insulation 5cm UFH Screed 4cm Tile 1cm
Your looking at 10cm of Concrete & optimum screed thickness is 65-75mm for ufh, 65mm minimum. Used a reinforce fibre screed & you could get away with 5cm.
Under the brick layer is a mixture of soil with large stones, almost like hardcore. Sandstone I believe. Thanks for the reply KIAB - presumably you must always use a hardcore - sand blinding base for any concrete floor?
Yes. You might be able to go down safely another 150mm, but it could involve you end up underpining the foundations, without seeing it very difficult to say, you definitely need a second opinion of a structural engineer before doing any further work.
I agree, I wouldn't be digging out anything until a structural engineer has seen it, my monies on it needing to be underpinned before you go any further.
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