As the prospect of a loft conversion is a few years down the line, I'd like to reinforce the existing loft joists and add some extra height to them for an extra layer of insulation before boarding the entire thing in ply.
The existing build is 100years old, the loft is in two sections.
The cut roof with the 2" x 4" joists running front to back and supported by a stud spine wall in the centre. Max room length to the spine wall is about 5.5m into a bay window. Overall length approx 8.5m longest joist 6m, longest binder 6m.
Rear loft, the 2" x 4" joists run side to side with a span of 4m, sit on a wall plate on the outer wall and skew nailed to a ledger (trimmer joist) which is in turn supported on the party wall with steel brackets. One long binder of 6.3m. The ledger has started to fall/rotate very slightly with the weight of the joists and is about 5 degrees away from the vertical. The bottom end of the joists on the ledger are notched to accommodate a 1 inch square batton that runs along the bottom of the face of the ledger (much like notch for galvanised wall hangers).
So far I hope all clear. The rear loft causes me more concern than the main although it's been supporting a very large galvanised water tank, so it's not going to fall down exactly. My concer is that the joists ends where held in place with skew nails, sometimes just the one, and the joists have shrunken away from the ledger in places.
At the moment all the ceilings are down which makes life easier.
The idea so far for the rear loft. To double up the existing joists with C24s creating 4" x 4"s. I can't use T to T hangers on the ledger end, there's no space as the joists will be next to each other, if I leave a gap to accommodate galvanised brackets then there’s no space for a run of insulation. due to the skew of the ledger the brackets would also require persuasion to sit level and do their job. C24s of metric will also be slightly smaller than imperial 2/4s, so without faffing about packing the ends I’d have uneven joist levels. Wall plate end; simple. Ledger end skew screwed with the assistance of some galvanised brackets/restraint strapping, which is about the best I can do.
Ledger/trimmer joist gets some additional M12 bolts with chemical anchors to be on the safe side – it’s in very soft London Stocks, so you have to be careful or they’ll fail.
Front much like the rear, doubling the 2" x 4"s to become 4" x 4"s with some solid strutting where the ceiling boards join. I have about 8 joists that are 6m long, with only a binder for intermediate support, so you can see why I’d want to increase size V span. The rest are just 3.6m lengths. I can’t put in deeper joists of say 220mm parallel to the existing ones to give me height, due to rafter plates and how the bay gable end is integrated into the joists ends, or this would be a nice easy solution.
So far so simple-ish.
Here’s where it get s a little more tricky. I want to add height and make the party walls take some of the weight rather than the stud spine one.
My options are therefore either new ledgers on either party wall with strapped hangers or masonry joist hangers directly in the walls. The second level of new joists would be at 90 degrees to the first. The span of the building width is 6m, so the problem is one of the recommended span/C24 dimensions, and the fact the lengths will have to be x2 3.6m overlapped and joined, I can’t get a single length in. If I adhere to Span Tables, it’d be a very big long joist.
My perspective is that the original joists (now reinforced) will take some of the weight of the new joist layer above and the new additional ply flooring, so I don’t have to be that paranoid. Clearly it’s a loft so overall height/weight of new material is a consideration.
I’m toying with the idea of using 2”x4” lengths once again, due to cost, weight, ease of installation and the fact they’re supported at 12” intervals by the lower 4” joists. The existing 5.5m ones have been supporting reasonable weight with no issues, but clearly it’s not what I’d choose in an ideal world.
Perspectives much appreciated.
The existing build is 100years old, the loft is in two sections.
The cut roof with the 2" x 4" joists running front to back and supported by a stud spine wall in the centre. Max room length to the spine wall is about 5.5m into a bay window. Overall length approx 8.5m longest joist 6m, longest binder 6m.
Rear loft, the 2" x 4" joists run side to side with a span of 4m, sit on a wall plate on the outer wall and skew nailed to a ledger (trimmer joist) which is in turn supported on the party wall with steel brackets. One long binder of 6.3m. The ledger has started to fall/rotate very slightly with the weight of the joists and is about 5 degrees away from the vertical. The bottom end of the joists on the ledger are notched to accommodate a 1 inch square batton that runs along the bottom of the face of the ledger (much like notch for galvanised wall hangers).
So far I hope all clear. The rear loft causes me more concern than the main although it's been supporting a very large galvanised water tank, so it's not going to fall down exactly. My concer is that the joists ends where held in place with skew nails, sometimes just the one, and the joists have shrunken away from the ledger in places.
At the moment all the ceilings are down which makes life easier.
The idea so far for the rear loft. To double up the existing joists with C24s creating 4" x 4"s. I can't use T to T hangers on the ledger end, there's no space as the joists will be next to each other, if I leave a gap to accommodate galvanised brackets then there’s no space for a run of insulation. due to the skew of the ledger the brackets would also require persuasion to sit level and do their job. C24s of metric will also be slightly smaller than imperial 2/4s, so without faffing about packing the ends I’d have uneven joist levels. Wall plate end; simple. Ledger end skew screwed with the assistance of some galvanised brackets/restraint strapping, which is about the best I can do.
Ledger/trimmer joist gets some additional M12 bolts with chemical anchors to be on the safe side – it’s in very soft London Stocks, so you have to be careful or they’ll fail.
Front much like the rear, doubling the 2" x 4"s to become 4" x 4"s with some solid strutting where the ceiling boards join. I have about 8 joists that are 6m long, with only a binder for intermediate support, so you can see why I’d want to increase size V span. The rest are just 3.6m lengths. I can’t put in deeper joists of say 220mm parallel to the existing ones to give me height, due to rafter plates and how the bay gable end is integrated into the joists ends, or this would be a nice easy solution.
So far so simple-ish.
Here’s where it get s a little more tricky. I want to add height and make the party walls take some of the weight rather than the stud spine one.
My options are therefore either new ledgers on either party wall with strapped hangers or masonry joist hangers directly in the walls. The second level of new joists would be at 90 degrees to the first. The span of the building width is 6m, so the problem is one of the recommended span/C24 dimensions, and the fact the lengths will have to be x2 3.6m overlapped and joined, I can’t get a single length in. If I adhere to Span Tables, it’d be a very big long joist.
My perspective is that the original joists (now reinforced) will take some of the weight of the new joist layer above and the new additional ply flooring, so I don’t have to be that paranoid. Clearly it’s a loft so overall height/weight of new material is a consideration.
I’m toying with the idea of using 2”x4” lengths once again, due to cost, weight, ease of installation and the fact they’re supported at 12” intervals by the lower 4” joists. The existing 5.5m ones have been supporting reasonable weight with no issues, but clearly it’s not what I’d choose in an ideal world.
Perspectives much appreciated.
