sister joists deep enough?

18 Jul 2011
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United Kingdom
Hello all
Our loft conversion company used sister joists to level off part of the floor which they had built a bit wonky. There was a 3 cm fall over a length of 2 metres.
The floor is now fairly level overall but slopes a little bit here and there. We can live with it and are happy with the room and now have a nice laminate down.

I'm just wondering if its ok to put heavy furniture on the part of the floor that was leveled?
the sister joists are about 90mm deep and the initial joists are about 125 or maybe even 150mm deep. The joists and sister joists are both about 45mm wide I think.
We have had a big desk there for a couple of months as well as me and my computers and so far no signs of any sagging. We would also like a couple of tall bookcases in that part of the room but wondered if that is pushing it a bit?
I've attached a couple of pics
thanks in advance for any advice
joists1.jpg joists2.jpg
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If you are worried about sagging floors in a loft conversion you should have employed a better builder! It's all been done to regs etc presumably?
we certainly should've employed a better builder. with the benefit of hindsight we should've used someone else. Its been signed off recently but the joists were never inspected. It took ages to get signed off. Things that had to be corrected were missed by the inspector and it was me who pointed it out to him and sent pictures. He then told the builders to come back and fix things. I didn't remember to send pictures of the floor joists to the inspector as I didn't have time to supervise the whole job as I was working. the project manager was supposed to do that but he was never here.
Your loft floor is something else - you've been putting it down and taking it up for what: 6 months?

Its still not right -
One, there was no need to sister to gain the height,
And two, you need far more screws in a W pattern, and construction glue in the join.
And three, there doesn't seem to be any appreciable difference with the 2" x 4's clapped on the 2" x 6's?
Sistering always runs the risk of squeaks - far better to pack up off the top of the joist.
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Sistering on one side of the joist is going to twist the joist when there is a load ( floor board and furniture ) pressing down on the sister. Put one each side to prevent the twisting action of a single sided sistering.
thanks for reply folks, much appreciated. As they didn't sister on each side of the existing joist I'll avoid putting any heavy furniture in that part of the room.
the photos are a couple of months old Vinn, I've been meaning to post for ages but not had chance. The loft conversion did go on forever but the floor was only amended once in the bedroom. The sister joists are about 1 cm higher in the far left corner, and 3cm higher in the far right near the radiator. I didn't manage to get a picture of all the sister joists. The didn't do a W pattern with bolts and didn't use construction glue either

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