Spindly joists

[Anonymous]

You may rememeber my question about "live floors"?

So up came the floor.

The issue seems to be that the central joists have to span too long a distance. The end of the room is a semi circle and at this point is probably 24' end to end. The joists are only 9" deep and 2.5" wide, spaced 15" apart, with 2 runs of noggins (which are all still fine).

Mackays would seem to suggest that for a 24' room, the joists would be c. 14" deep, so these are a little on the small side...

Now - its true that its lasted all these years but whats clear is that its never been acceptable - the central joist has had planks nailed along side its length between the noggins to try to stiffen it. The ceiling underneath it has had a#####false ceiling screwed over the top which we want to remove.

So, its time to fix it!

One option is an RSJ in the room below (!) I guess (shades of NADFAS...) but pehaps I can brace the existing joists with steel angles, which would remain hidden inside the floor void?.

I would very much welcome any ideas - we are going to use a structural enginneer for final specs but it will help to have some good ideas first?

Many thanks
Craig

 

[Anonymous]

I'm no engineer so hopefully others will oblige with more info - but this house is sounding fascinating! If you see someone skulking around next week it may well be me (you can tell as I'm the one with lime plaster in her hair and filthy fingernails...)

 

[Anonymous]

As well as doing the final spec, the Structural Engineer will be able to give you several options and then you can decide which way to go.

 

[Anonymous]

As DMC says, the structural engineer is the guy to suggest solutions to this one for you. But - just to feed the ideas pot - have you got the headroom to put a substantial cross-joist underneath and at 90 degrees to the existing ones (supported either on joist hangers or on posts)? This would effectively halve the span of the existing joists.

 

[Anonymous]

A relatively simple way of providing additional stiffness to the joists would be to bolt steel flats to both sides of each joist - these would be drilled in pairs before installation, offered up, and the joist drilled for through bolts. Of course the exisiting strutting would have to go, and you could have problems with any pipes / cables which run in the floor void. This method has the advantage that it would be invisible once the floor was reinstated, and need not disturb the room below. At a guess I'd say that 150 x 10 flats would be about right, maybe bolted through at 500 centres - your engineer will do the sums. Getting a 6m length into position might pose a few problems...

 

[Anonymous]

Thanks for the replies.

It looks like the original lath ceiling below (currently hidden beneath a false ceiling of plasterboard nailed on batons) is toast and will need to be replaced. So I will have access to the joists from below where I can probably achieve more.

There might be room for an RSJ but it would be quite intrusive, so the plate idea (or even angle irons rather than plates?)

 

[Anonymous]

Well, I would shake your hand but the skinned knuckles and cuts make it too painful...

 

[Anonymous]

a couple of thoughts,

You could strengthen the existing joists by "gluing and screwing" say 50mm or 75mm deep battens to the underside or even on top of the joists. Additional joists could also be placed between the existing ones.

A good connection (ie plenty of nails or screws) between the joists and the floor boards will also increase the capacity. Don't ask the engineer to do a calculation for this as it is difficult to put numbers to and he will probably start crying.

The plate idea will work but the engineer will need to check the detail at the support i.e will the steel plate need to bear onto the wall, if it does it will be awkward.

Although it doesn't look symmetrical one properly designed plate on only one side of the joist will work.

The RSJ running at 90 degrees to the joists is worth developing. If headroom is a problem this new RSJ could be placed within the depth of the existing joists.....i.e prop the joists.......create 2 cuts say 150mm apart......place RSJ....and connect the joists to the RSJ with suitable joist hangers. The bottom of the RSJ can be at the same level as the bottom of the joists.

Good luck