sagging floor joists

20 Mar 2010
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West Midlands
United Kingdom
Hi, hope someone can help,

I'm renovating a property built in 1896, in one of the rooms (first floor) the floor has sagged by over 40mm over a 4.7 metre span,
the joist sizes are 175mm X 63mm.

I will be boarding and plastering onto these joists (ceiling), also the staircase to the second floor rests on these same joists and the stairs slope from left to right by about 10mm.

I was wondering what my options were,

Was thinking,
1) remove and replace joists to the current regs,
2) screw timber along the joists to give me a straight edge for the flooring and ceiling,
3) leave it as it is

Thanks for any help
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I can't see any other options and by the time you mess about packing the floor on both sides it may be as easy to put new joists in and have a level floor.
Is there any mid-span or 1/3rd span solid or herring-bone bracing?

If not add some as part of any other floor joist remedial work.
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Thank you all for your help ;)

unfortunately I made a schoolboy error, yesterday I measured this 'sagging' by using a spirit level on the floor from one side of the room to just past the middle of the room,
however, today I used my water level from one side of the joist to the other and found a difference of 30mm, and double checked it using a laser level,
so, the joists are actually sloping :rolleyes:
Most of the joists are resting on an eight foot wide wooden lintel which is above a widow (shop)

So the plan now is to jack up the joists and fit a concrete lintel along side the original wooden one, this should leave the joists sagging by about 10mm which I could put up with.

I will be adding some bracing and possibly a false ceiling to give it a perfect level plus extra fire and soundproofing .

sorry about the cock-up
1. The difficulty you have is that your joists are undersized for the span. and if you go for the correct depth joistings then you either have to raise the floor ( FFL ) or drop the ceiling height.

2. By using 2 x acrows and a plank you can jack the floor level, but now you have the decision as to wether you remove the ceiling or lift the T&G flooring to gain access for stiffening the in-situ joists, and as noseall mentioned, strengthening cross or block bracing.

3. To stiffen a floor can be done by sistering, say 25mm ply rippings on either side of the joist - there's a massive literature on this subject if you google.

4. Jacking the floor can loosen the joist tails in their bearing pockets!

5. If you go for a complete floor removal, then run steel midway as a support beam. There is a way of slipping the steel in at a central/cutjoists position without much disturbance, but it's not for DIY.

6. Whatever you do will involve much dusty work, and two or more workers

7. All pipework and cables must be taken into account.
I composed my post at about 1800hrs but didn't post it until later without, of course, seeing your last post.
Very informative post tim,

I should of mentioned that I have removed all plaster in the whole building and there is no pipework or electrical cables in this room so moving/removing the joists shouldn't be a major problem apart from the joist that the staircase is sitting on.

I can't have deeper joists because I can't raise the floor (mainly because of the staircase) and the joists have to sit on a lintel, and to lower this lintle would mean the replacement of the shop window.

I can however fit a support beam, I will have to get a party wall agreement but I don't see a problem as the next door neighbour is very happy to see this property being renovated, but I'll only do this if I end up replacing the joists.

I'm going to jack up, pack and brace the joists, and I'll look into this 'sistering' you mentioned.

Thanks, I'll let you know how I get on
Thinking outside the box, is 30mm over nearly 5m something to worry about? Or for that matter 10mm of sag over 5m? All in all that sounds pretty good to me.

Obviously if you have issues with bounce in the floor thats diffrent but otherwise while they might not meet modern regs they arnt going to fall down.


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