osprey Posted October 4, 2023 Share Posted October 4, 2023 I want to insulate under a suspended wooden floor of a 1920s house. No alternative but to lift floorboards, which will destroy them. The question I have is: what is the best replacement? Current original floorboards are 22mm thick. Skirting boards are large, and will not be removed. I have done one smaller room and used 22mm chipboard from Wickes, but since have seen lots of reports of squeaking using this board. I have it slightly in one place so far, but dread it in a larger, more frequently used room. So for a robust squeak- free floor, what do I use: OSB, ply, chipboard, new softwood boards, other? Cost needs to reasonable. Room is about 5 x 4m. Floor currently carpeted, and will remain so. Thanks. Link to comment Share on other sites More sharing options...
Redbeard Posted October 4, 2023 Share Posted October 4, 2023 (edited) Lifting the boards need not destroy them. The last floor I insulated from above we punched every single nail down into the joists using a parallel-sided punch. We allowed for 20% wastage (destroyed boards) and finished with less than 10%. It's a b**l-ache, but very doable. It probably took 2 of us half a day for a 32m2 floor to lift the boards. Edited October 4, 2023 by Redbeard Clarity Link to comment Share on other sites More sharing options...
Marvin Posted October 4, 2023 Share Posted October 4, 2023 I wonder if people are using the D4 flooring adhesive? I have used D4 on about 150 square meters of 22mm chipboard tongue and groove(T&G) boarding with no problem. I also use screws about 3 times the length of the chipboard and 22mm moisture resistant T&G boards. https://uk.westfraser.com/our-products/caberfix/caberfix-d4/ Link to comment Share on other sites More sharing options...
Marvin Posted October 4, 2023 Share Posted October 4, 2023 (edited) I have also insulated suspended timber floors by cutting hatches in the floor and crawling underneath installing 100mm PIR between joists and 50mm PIR across all the joists held up with battening. All gaps foam filled. A better choice if there is enough room below the floor and you have to do the whole ground floor which is inhabited. W e just lifted a corner of the carpet cut holes in the right places and off you go. It took 2 people 7 days each to do 100m2. Edited October 4, 2023 by Marvin Link to comment Share on other sites More sharing options...
FuerteStu Posted October 4, 2023 Share Posted October 4, 2023 The reason cheaper materials often squeek is because the joists are uneven. If one is 3mm lower then pressure on the board above causes movement. I've laid several osb tongue and groove floors that are silent Link to comment Share on other sites More sharing options...
joe90 Posted October 4, 2023 Share Posted October 4, 2023 (edited) +1 to tongue and groove OSB and laid with d4 glue and screws, completely silent!!! Most floorboard floors squeak because the board shrinks thickness wise and the nail is no longer tight and the squeak is the board going up and down the nail, I have silenced many a floorboard by punching existing nails tighter into the boards. Edited October 4, 2023 by joe90 Link to comment Share on other sites More sharing options...
Sparrowhawk Posted October 4, 2023 Share Posted October 4, 2023 1 hour ago, Marvin said: I wonder if people are using the D4 flooring adhesive? I have used D4 on about 150 square meters of 22mm chipboard tongue and groove(T&G) boarding with no problem. I also use screws about 3 times the length of the chipboard and 22mm moisture resistant T&G boards. https://uk.westfraser.com/our-products/caberfix/caberfix-d4/ I've seen glue mentioned on this forum a few times, and my thought is "what happens when you need to lift them?". T&G is bad enough, but if glued as well is this not a install-only process which will cause problems for future maintenance? Link to comment Share on other sites More sharing options...
Conor Posted October 5, 2023 Share Posted October 5, 2023 12 hours ago, Sparrowhawk said: I've seen glue mentioned on this forum a few times, and my thought is "what happens when you need to lift them?". T&G is bad enough, but if glued as well is this not a install-only process which will cause problems for future maintenance? Quite often, cutting a hatch through a board is easier than lifting an entire sheet, even if this just screwed down. 10mins with a multi tool and you're in. 2 Link to comment Share on other sites More sharing options...
ProDave Posted October 5, 2023 Share Posted October 5, 2023 16 minutes ago, Conor said: Quite often, cutting a hatch through a board is easier than lifting an entire sheet, even if this just screwed down. 10mins with a multi tool and you're in. And 2 hours to fix the leaking pipe when you "discover" an unknown pipe that is touching the bottom of the board. When boarding my new build with P5 chipboard, at each end of each room, I left a half board wide strip, that has part of the tongue planed off and cut into shorter strips that gives an access trap anywhere you want at each end of the room. It should be possible for example then to fish cables to anywhere in the room. The access traps are screwed down with no glue. 1 Link to comment Share on other sites More sharing options...
osprey Posted October 5, 2023 Author Share Posted October 5, 2023 Thanks all for replies. When people are saying 'glue' with chipboard, is that for just the t&g? I have read of people gluing the sheets to the joists as well... Those using OSB: I can only find 18mm t&g. Did you use t&g? I would have to add 4mm to the joists I guess. Any DISadbpvantage to using OSB? Chipboard seems to be the 'standard' even for (cheaper) newbuilds. What screws do people use? There are special ones for flooring chipboard, with a smooth part at the top, 'to make boards be pulled to the joists firmly'. Other people say fully threaded. Other suggestions: I don't have access from below. Interesting idea about punching nails down. Will think about it. Link to comment Share on other sites More sharing options...
osprey Posted October 5, 2023 Author Share Posted October 5, 2023 On 04/10/2023 at 18:02, Marvin said: I wonder if people are using the D4 flooring adhesive? I have used D4 on about 150 square meters of 22mm chipboard tongue and groove(T&G) boarding with no problem. I also use screws about 3 times the length of the chipboard and 22mm moisture resistant T&G boards. https://uk.westfraser.com/our-products/caberfix/caberfix-d4/ Just looked at that site, very useful. Just a thought, If screws cause the squeak, and you glue t&g sheets together, do you actually NEED screws? Just have a floating floor? Link to comment Share on other sites More sharing options...
joe90 Posted October 5, 2023 Share Posted October 5, 2023 16 minutes ago, osprey said: If screws cause the squeak, Screws will not cause a squeak if tight, on my last build all the l first floor was glued and only screwed along one wall to start and completely silent, Link to comment Share on other sites More sharing options...
osprey Posted October 5, 2023 Author Share Posted October 5, 2023 26 minutes ago, joe90 said: Screws will not cause a squeak if tight, on my last build all the l first floor was glued and only screwed along one wall to start and completely silent, Thanks. Link to comment Share on other sites More sharing options...
Onoff Posted October 5, 2023 Share Posted October 5, 2023 The Police lifted the floorboard for me in my first house when I found bones under the suspended floor. Did a lovely neat job. Must have been proud of their work as they took loads of photographs. 2 Link to comment Share on other sites More sharing options...
joe90 Posted October 5, 2023 Share Posted October 5, 2023 1 minute ago, Onoff said: The Police lifted the floorboard for me in my first house Did they put them back? Link to comment Share on other sites More sharing options...
FuerteStu Posted October 5, 2023 Share Posted October 5, 2023 1 hour ago, joe90 said: Did they put them back? The bones? Bit creepy 1 Link to comment Share on other sites More sharing options...
osprey Posted October 6, 2023 Author Share Posted October 6, 2023 22 hours ago, Onoff said: The Police lifted the floorboard for me in my first house when I found bones under the suspended floor. Did a lovely neat job. Must have been proud of their work as they took loads of photographs. Hmm, might try that. Link to comment Share on other sites More sharing options...
Onoff Posted October 6, 2023 Share Posted October 6, 2023 On 05/10/2023 at 19:12, joe90 said: Did they put them back? I said it was OK, I'd do it. In reality it was really handy as I wood treated all the joists. Some boards were broken but back then I was getting them milled up to size by the local wood yard. 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted October 7, 2023 Share Posted October 7, 2023 Get the right type of screws. Link to comment Share on other sites More sharing options...
osprey Posted October 8, 2023 Author Share Posted October 8, 2023 (edited) I have seen that type of screw advertised, but I have not heard if they work. I have seen the theory that a screw with a smooth section above the thread helps in pulling the sheet to the joist firmly. I am not sure how the top thread in that screw works. Edited October 8, 2023 by osprey Link to comment Share on other sites More sharing options...
SteamyTea Posted October 8, 2023 Share Posted October 8, 2023 15 minutes ago, osprey said: am not sure how the top thread in that screw works The top thread stops the floor board/sheet moving, while the lower thread locates it on the joist. If there is a gap, the board/sheet cannot move downward. The 'squeaky board' sound is rubbing on the screw/nail shaft, not wood on wood, usually. You can get a similar effect using bolts, rather than screws. Just need to drill a clearance hole and make sure the heads are larger diameter so that they don't pull through. 1 Link to comment Share on other sites More sharing options...
Onoff Posted October 8, 2023 Share Posted October 8, 2023 2 hours ago, osprey said: I have seen that type of screw advertised, but I have not heard if they work. I have seen the theory that a screw with a smooth section above the thread helps in pulling the sheet to the joist firmly. I am not sure how the top thread in that screw works. Yes they work. I used Spax floorboard screws. They're excellent. 22mm chipboard floor. As solid as, no squeaks. https://www.screwfix.com/p/spax-tx-countersunk-self-drilling-flooring-screw-4-5mm-x-60mm-300-pack/88716? 1 Link to comment Share on other sites More sharing options...
osprey Posted October 20, 2023 Author Share Posted October 20, 2023 (edited) Thanks, intereting they work, but I am not sure how. The e.g. Spax screws have two different threads. I assume the lower, coarse one bites into the joist first. The screw then goes into the joist until the fine thread reaches the chipboard. The next couple of turns of the coarse thread would be sufficient to pull the board in tight, but the fine thread would be 'travelling' more slowly (taking maybe four turns to travel the same distance). Would it not just rip its way through the chipboard? Edited October 20, 2023 by osprey Link to comment Share on other sites More sharing options...
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