Floor joist against wall?

[gasbusters]

Can a new loft floors 1st joist be fitted directly against the brick wall or as ive done hear, bolt it directly to the wall?

Ive been told be someone who had thetes done there should be a gap of 40mm between this structural timber and the wall?

If this is the case can someone explain why?

 

[Deleted member 174758]

You need the gap to prevent moisture wicking from the wall and potentially causing wet rot in the floor edge/joist, also stops dry rot from transferring into the floor structure on older buildings (where, believe me, it is an issue) and finally is better in terms of soundproofing - noise transmits far easier through abutting solids than it does across an air gap. If you must fix a ledger to a wall, especially an exterior one or one below ground level, make sure that you use treated timber and fix some DPM (e.g. 1000 gauge Visqueen) between the timber and the masonry

 

[gasbusters]

You need the gap to prevent moisture wicking from the wall and potentially causing wet rot in the floor edge/joist, also stops dry rot from transferring into the floor structure on older buildings (where, believe me, it is an issue) and finally is better in terms of soundproofing - noise transmits far easier through abutting solids than it does across an air gap. If you must fix a ledger to a wall, especially an exterior one or one below ground level, make sure that you use treated timber and fix some DPM (e.g. 1000 gauge Visqueen) between the timber and the masonry

Would the same issues arise in the loft?

The pic above is in my loft, the beams bolted directly to the wall, i did this on the assumption it would give extra strength to the wall, but then was told this may be against building regs.

I guess i may have to cut those bolts and move that beam.

I have about 2cm on the bolts, could i just move that beam away from the wall 2 cm and leave it bolted to the wall or do those bolts have to come out as well as sound could potentially transfer between from beam to bolt to wall?

 

[Deleted member 174758]

Would the same issues arise in the loft?

If the wall is an outside wall in particular, then yes, especially if the building was erected prior to modern cavity walling (you can tell I work mainly on old buildings these days can't you). As to timber giving extra strength, I somehow doubt it - masonry walls are "glued" together with mortar, but it's their mass (weight) which keeps them put. If the wall does bow outwards I doubt that a 2in thick C16 joist would make a lot of difference to that happening

I have about 2cm on the bolts, could i just move that beam away from the wall 2 cm and leave it bolted to the wall or do those bolts have to come out as well as sound could potentially transfer between from beam to bolt to wall?

If you do that then the bolts won't be doing anything will they? Assuming that the joist ends are sitting in what looks like a steel RSJs (rolled steel joists or "I" beams) then why would the end joist need to be connected to the wall at all? If you want more rigidity in the floor you'd be as well off having solid blocking between all of the joists at the wall root where the joists are carried in the steels

 

[gasbusters]

If the wall is an outside wall in particular, then yes, especially if the building was erected prior to modern cavity walling (you can tell I work mainly on old buildings these days can't you). As to timber giving extra strength, I somehow doubt it - masonry walls are "glued" together with mortar, but it's their mass (weight) which keeps them put. If the wall does bow outwards I doubt that a 2in thick C16 joist would make a lot of difference to that happening

So my typo mistake, i meant to say i bolted the wooden beam (c24 75mm x 200mm) to the wall in the hope it would give the joist more strength and rigidy if it was bolted to the wall.

That wall is a party wall with neighbours house

If you do that then the bolts won't be doing anything will they? Assuming that the joist ends are sitting in what looks like a steel RSJs (rolled steel joists or "I" beams) then why would the end joist need to be connected to the wall at all? If you want more rigidity in the floor you'd be as well off having solid blocking between all of the joists at the wall root where the joists are carried in the steels

No, the bolts wont be doing much if i pull the joist away from the wall.

Those joists are sitting on steel i beams, the joists are notched and about 60mm of the joist will be sitting on the beam either end.

I will be putting noggings between the joists, all joists will be at 400mm centres between joists.

Are you saying i can put a nogging either end off the beam thats at the wall, so a nogging/block of wood between the joist and the party wall?

 

[gasbusters]

This is the steel beam, one on either end of the loft

 

[Leofric]

To bldg. regs - 50mm gap between joist and wall with timber packing blocks in gap.

 

[Deleted member 174758]

Are you saying i can put a nogging either end off the beam thats at the wall, so a nogging/block of wood between the joist and the party wall?

What I was trying to convey was that you need to infill the gaps between the joists at the RSJs with solid blocking (what you called "noggings" - sorry, but in my world a "noggin" or "dwang" is generally inside a stud wall). This stops joists from twisting or moving under load and makes for a stiffer, less bouncy floor. I normally toe nail (I.e nail at an angle) the blocking into the abutting joists, but generally leave out the end blocks between the last joist at each end and the masonry walls because they might allow moisture bridging leading to rot, just like bolting an unprotected joist to an exterior wall can

 

[Deleted member 174758]

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