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Roof ceiling joist strengthening.


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hi,

looking to put new plasterboard on first floor ceiling but my ceiling joist ar sagging quite a lot in the middle, the struts are pushing them to sag. i have 3 struts each side, as in pictures.

Could you give me advice if it's ok if i put 2 acrow props for each side to hold purlin then cut two struts which is parallel to each other, then sister joist ( only the ones is holding strut) with same 3x2 c24 timber, level them up. Add shims where brick wall goes in the middle under joist. And then make same strut with new timber on now doubled 3x2. and then move to another two struts.

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There will be others who know more than me. But I would be worried about the integrity of the joists tbh and would probably spend a few quid to get a structural engineers report. If I read you post right the joists are 3 by 2 which seems really undersized looking at the span, significantly so tbh. Just looking at the pic I can feel the strain in the joists lol.

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The above is sound advice.

I am guessing the diagonal props were introduced to help support sagging rafters (again guessing slates removed and replaced with tiles) so increased weight on rafters.

I am also thinking a wall has been removed which would have helped Support the ceiling and rafters.

 

 

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6 minutes ago, markc said:

The above is sound advice.

I am guessing the diagonal props were introduced to help support sagging rafters (again guessing slates removed and replaced with tiles) so increased weight on rafters.

I am also thinking a wall has been removed which would have helped Support the ceiling and rafters.

 

 

Yes if there was a wall below supporting the joists I would sense them breathing a sigh of relief ? 

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1 hour ago, alexbr said:

hi,

looking to put new plasterboard on first floor ceiling but my ceiling joist ar sagging quite a lot in the middle, the struts are pushing them to sag. i have 3 struts each side, as in pictures.

Could you give me advice if it's ok if i put 2 acrow props for each side to hold purlin then cut two struts which is parallel to each other, then sister joist ( only the ones is holding strut) with same 3x2 c24 timber, level them up. Add shims where brick wall goes in the middle under joist. And then make same strut with new timber on now doubled 3x2. and then move to another two struts. imageproxy.php?img=&key=f5f06bfe2c42e69c

 

If it was me, and I had gone this far, I would attach 2x4's to the side of the existing, levelled throughout. Find the lowest point and measure everything from that. A laser level would be your friend here. 

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There is a wall, in the middle and on the ground floor there is rsj beam, where wall goes, but it  looks like was there long time a go   I had engineer, still waiting for calculations from him. He advised me to sister the joist.

IMG_20211216_141823.jpg

IMG_20211216_142327.jpg

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4 minutes ago, Carrerahill said:

If it was me, and I had gone this far, I would attach 2x4's to the side of the existing, levelled throughout. Find the lowest point and measure everything from that. A laser level would be your friend here. 

ceiling is quite low in some places, and sagging is 4cm-5cm, 

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Ah, could not see the wall In the first pic!. I think the purlins have sagged a bit and those diagonals have pushed the ceiling down, why not cut those diagonals, Jack the ceiling up (if it will go) and re Instate the diagonals and if necessary use metal strapping hanging the ceiling joists from that purlin. Is your roof bowed looking  from the outside? Is the purlin straight? Yes you could just sister those ceiling joists with 4x2 level with the lowest part rather than the above. 

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6 minutes ago, joe90 said:

Ah, could not see the wall In the first pic!. I think the purlins have sagged a bit and those diagonals have pushed the ceiling down, why not cut those diagonals, Jack the ceiling up (if it will go) and re Instate the diagonals and if necessary use metal strapping hanging the ceiling joists from that purlin. Is your roof bowed looking  from the outside? Is the purlin straight? Yes you could just sister those ceiling joists with 4x2 level with the lowest part rather than the above. 

It's a bit bowed but not a lot, a lot house's on the street same..

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18 minutes ago, joe90 said:

I think the purlins have sagged a bit and those diagonals have pushed the ceiling down,

Agreed. Undersized rafters  (perhaps the roof load has increased if retiled) and the diagonal struts may have been added as a bodge, but are now bending under the load they were not meant to take.

 

I would not adjust and leave it as is. 

 

Either fix new, deeper, timbers against the existing joists but horizontally, (lots of fixings) so that they strengthen them and also provide a level for the ceiling. (sistering, as above)

 

OR prop up the whole roof and replace the joists and the struts with much heavier timbers.

 

OR get an Engineer in.

 

I think if you were just to board over, or fix a new level surface underneath first, that it might continue to deflect.

 

Now looking again at the photos, I see the attic joists are lapped near the middle. Looks like several issues over the years and now is a bit of a mess.

 

 

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19 hours ago, alexbr said:

ceiling is quite low in some places, and sagging is 4cm-5cm, 

So start there and sister them all with level 2x4's - quite a common way to level a ceiling. You can also counter-batten and shim but that is probably more work, but cheaper. 

Edited by Carrerahill
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16 hours ago, alexbr said:

...and should i do all of them or every other?

All of them or you will have too big a spacing for fixing PB then will end up with sagging plasterboard!

 

You are beginning to sound like a contractor trying to cut costs at every turn! ?

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1 hour ago, Carrerahill said:

All of them or you will have too big a spacing for fixing PB then will end up with sagging plasterboard!

 

You are beginning to sound like a contractor trying to cut costs at every turn! ?

? no, 

i got a lot 2x3, so was thinking to use 2x4 , where struts is pushing ceilings and in other places somehow use 2x3, if not will get more 2x4 not a problem

 

 

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3 minutes ago, alexbr said:

yes in the middle

Well if you want to do as little as possible structurally I would just screw and glue 4x2 alongside the existing 3x2, level on the bottom at the lowest point and level across the room in both directions,  no point in fixing to walls etc . Do this on every one, will strengthen them a lot and give you a flat surface to plasterboard too.

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This was a common enough roof structure back in the day., when times were tight and standards were more of wing and a prayer affair. 3x 2 ceiling joist spanning what looks like say 12’, while also taking the load from struts to rafters lol. You wouldn’t dream of it now. It isn’t likely to fall down just deform more and more over many years. The struts were supposed to go close to a wall but this was poorly interpreted at times as we see.
 

To sort it proper would be expensive ie steel purlins (shims to rafters) with hangers and runners to support the ceilings. I don’t think it practicable to reverse the deformation in rafters but ceiling joists should be quite doable. Then with the addition of hanger & runner the existing ceiling joist spans should be reasonable. I would guess this will be the engineers solution. An alternative would be to fabricate a deep timber lattice beam including the hangers and faced with ply sheeting. Engineers might shy away from this as it would require more structural design on their part but may be my preferred choice. 

Edited by Gordo
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21 hours ago, joe90 said:

Well if you want to do as little as possible structurally I would just screw and glue 4x2 alongside the existing 3x2, level on the bottom at the lowest point and level across the room in both directions,  no point in fixing to walls etc . Do this on every one, will strengthen them a lot and give you a flat surface to plasterboard too.

I would be careful about this solution. 4x2 would still be over spanned and deform. However if it was properly fixed to existing timbers this would be an improvement but still likely be over spanned (would need structural calculation to confirm). Adequate fixings of the two timbers to structurally work together would be problematic. The original structure would be considered sub-standard today, so much better to use new timbers which are much deeper to suit span, but that still leaves the rafters over spanned unless the new ceiling joists are designed to support the struts to rafters. Then the new ceiling joists are likely to be massive IMO

Edited by Gordo
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On 11/01/2022 at 14:38, joe90 said:

Well if you want to do as little as possible structurally I would just screw and glue 4x2 alongside the existing 3x2, level on the bottom at the lowest point and level across the room in both directions,  no point in fixing to walls etc . Do this on every one, will strengthen them a lot and give you a flat surface to plasterboard too.

so got email from engineer to double them with 2x6, and change binder to 2x6.

Could you explain me how is " SPLICE THE CONNECTIONS WITH 1 METRE MIN SPLICED TIMBER SECTIONS" looks like. 

 

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