Is it possible to construct a timber floor that spans 5m between steels and takes some of the roof loading?
I know that I will need to pay an SE for a proper calc, but would like to check out the viability of loft floor construction with the technical experts here before I get that far. The loft conversion contractors I have had in seem to be saying contradictory things, and I want to avoid nasty surprises later down the road.
The house is 6m x 7.6m (internally to outer walls) semi with traditional rafter/purlin roof of 2"x4" rafters. But, even though there are some support struts from the purlin down onto them, none of the internal walls are truly load bearing, despite being brick they don't line up with the walls below. The obvious design is to run two steels across the 6m width and construct the floor off that. There are no lintels to worry about, however the chimney stacks on the party wall are 5m apart at joist level and both in use, hence avoiding these the clear span between steels will be 5m.
Looking at the Trada tables, 5m clear span under domestic loadings seems towards the limit of what you can do with timber but OK. The rafter spans, possibly doubled up with thicker sister rafters, will need supporting by queen posts which form the stud walls of the room. However positioning these supporting stud walls immediately above the steels results in both very limited storage space behind and useless low walls that no furniture will fit. It would be more useful for us to make the room smaller (say 4m not 5m), by constructing the supporting stud walls on the floor instead. But is this structurally possible?
Can be make use of our "not quite" load bearing wall like the original roof does? Would we need to put some more steel in there instead? I am worried that 5m spams of timber just won't take the extra roof loading. Any suggestions on best ways to approach this design very welcome.
I know that I will need to pay an SE for a proper calc, but would like to check out the viability of loft floor construction with the technical experts here before I get that far. The loft conversion contractors I have had in seem to be saying contradictory things, and I want to avoid nasty surprises later down the road.
The house is 6m x 7.6m (internally to outer walls) semi with traditional rafter/purlin roof of 2"x4" rafters. But, even though there are some support struts from the purlin down onto them, none of the internal walls are truly load bearing, despite being brick they don't line up with the walls below. The obvious design is to run two steels across the 6m width and construct the floor off that. There are no lintels to worry about, however the chimney stacks on the party wall are 5m apart at joist level and both in use, hence avoiding these the clear span between steels will be 5m.
Looking at the Trada tables, 5m clear span under domestic loadings seems towards the limit of what you can do with timber but OK. The rafter spans, possibly doubled up with thicker sister rafters, will need supporting by queen posts which form the stud walls of the room. However positioning these supporting stud walls immediately above the steels results in both very limited storage space behind and useless low walls that no furniture will fit. It would be more useful for us to make the room smaller (say 4m not 5m), by constructing the supporting stud walls on the floor instead. But is this structurally possible?
Can be make use of our "not quite" load bearing wall like the original roof does? Would we need to put some more steel in there instead? I am worried that 5m spams of timber just won't take the extra roof loading. Any suggestions on best ways to approach this design very welcome.
