Converting a loft into a new room, Bit By Bit

[GarryNutter]

My house was built in the 80,s by Winpeys. It has the common Flink Trusses.

The span front to back is 8M there are 8 trusess across the house spanning 4.5M. Im looking to convert the loft into a habitable room over a longish period of time as money permits.

What im looking for is the stages you need to go through to remove the spars of the trusses.

Thats the first bit i want to do.

Does any one have any pictures of a conversion from start to finish.

thanks

garry

[Peter Crosland]

You need building regulations approval and before that the services of a structural engineer.

Peter Crosland

[Steven Campbell]

Would be a good start. The owner is a regular poster here.

[manatbandq]

I don't believe that was a modern truss roof.

MBQ

[manatbandq]

My sister had this done and they basically built a whole new roof structure out of very substiantial timbers paralle to the trusses and tied to new timbers and steels in the floor. Only then were the old trusses removed.

MBQ

[John Rumm]

Nope it wasn't... having said that, some of the same approach may be possible. A trussed roof would probably have less cross members and tie beams to get in the way, and this may allow the introduction of the floor joists between existing trusses without actually changing any of them at that stage.

It would obviously be fiddly work however since you would be working among all the extra wood of the trusses. A 4.5m span is within the realms of possibility for a wood beam (or a flitch beam certainly). You would probably need more holes through the roof however to get them in there since any rotation or moving them about once in the loft is going to be pretty difficult!

The harder bit is making sure you have adequate support in place before you start trimming out the webbing of the trusses.

[Garry Nutter]

Thanks everyone, for the help. John your site is a aladins cave of information. Could i ask how do you arrive at the position of the Knee Wall.

As i only have 8 rafters i was going to sister a furthur 150*50 to each rafter, and tie them in at the top, to make a triangle. Could i get away with 150*50, coudnt find any information on the web of the correct size for this.

thanks

garry

[meow2222]

Is it not on then to remove the additional matchstick forest from just one truss, and add glued screwed additional depth to all 3 sides to bring it upto required strength, and once done move onto the next one?

NT

[meow2222]

I've more often seen 2x4 used on old houses. But you need to put in whatever the regs say now, for some reason.

NT

[John Rumm]

The wall is a load bearing wall and takes the place of the purlin that was removed from the front of the roof slope. So its position is chosen to be roughly mid span of the front rafters and not that far from the original purlin location. In reality it could go a few feet either way - its location is not that critical.

To answer questions like this you need to do (or get done) some design calculations based on the anticipated loadings. In many respects you would probably find it easier to build a new floor without connecting it in any way to the existing trusses. You could also take the same approach to supporting the roof, or you could look at ways of reusing some of original truss components. The difficult thing with the trusses is that they are only structurally strong in their complete form. They don't have much rigidity the moment you chop bits out of them (although they are probably strong enough to hold up the facias and soffits by themselves ;-)

150*50 is going to be well undersized for a floor at that span. It is probably more heavy than required for rafters though. Having said that it does depend on the type of roof and its pitch, and the spacings of the rafters. Note there is no need to maintain the same spacing as the trusses - you could insert more rafters if you wanted.

[John Rumm]

That might also work. Not having done a trussed roof I am not famillier with the range of methods used to deal with them. Building a new roof supporting structure in parallel to the old would seem like a safe option, but may well be more work than is actually required if you can reuse some of the existing stuff. It will also depend a bit on what sort of converison you are doing since in many cases you won't be keeping the triangle shape of the trusses due to dormers etc.

[meow2222]

Strikes me it would fit well with the idea of doing a bit as and when, as it wouldnt disrupt the ceiling, and wood could be used that could be carried up through the hatch. So one could do one truss at a time with no time constraints or mess. New wood added could be end jointed with a router and glued and screwed in place.

NT

[John Rumm]

With regard to the ceiling, you could also achieve the same result if you have new floor joists in place and then added noggings between them also nailed to the truss to support the span of the base of the truss. A bit like I did for the old ceiling joists after removing their tie beam here:

would also help retain some of the benefit of not completely coupling the new floor to the existing ceiling (from a noise transmission point of view if nothing else).

You may have fun trying to produce the calcs to convince a BCO that the result is structurally sound. They seem rather wary of any joints more complex than a nail these days! ;-)

[Garry Nutter]

I'm sorry i think i have confused everybody with my terms and what i want to do.

The Grand Plan Hope Ive explained better this time.

Due to money restrictions i would like to convert the loft to Habitable space eventually.

To-do this i will need to get a structural engineer to calculate to beam sizes to support the roof and a new floor. Ive consulted the structural guy and Ive got a set of drawings, dimensions and structural calculations for the two beams.

The beams are 152*152*37 UC steal. I think the 37 is the weight. On top of this beam will be 150*75 wood plate to support the knee wall and something to hang the joists of via joist hangers. Joists are specified as 175*50, to cover a span of 15ft, these are on

400 centers.

I plan to do it in this order

1st get the steel beams in and the joists between, get some flooring laid in the joists to work off. Reinforce the roof rafters Build the knee wall Check every things okay

Cut out the old timbers Stop praying.

Questions Looking at Johns site

4th picture from the bottom. John how did you arrive at the size and position for these timbers which link the roof rafters together?

As i have fink trusses "w" shape made from 4.5 by 1.5 inch timber, i plan on screwing or bolting and gluing together a 150*50 timber to the side of every roof joist. Do you think this will be strong enough ?

That should do it for now possible further questions later.

Thanks

Garry

[John Rumm]

OK, perhaps an ASCII art layout of the beams may help us to visualise things...

or even something like:

1st get the steel beams in and the joists between,

You may have difficulty getting flooring in there with all the truss webbing in place... then again that depends a bit on the type of trusses you have.

Oh that is the fun bit... (in fact the most fun I have had with a chainsaw in ages ;-)

What, this one?:

to get some bearings on the shot, you are looking up toward the ridge of the roof, where the front slope meets the flat roof of the rear dormer.

The rafters under the slope are spaced at 400mm centres - this was to match the existing rafters. Some of them are old, some were new where the original ones were not long enough to meet the extended ridge beam (remember it used to be a hipped roof). (In the photo you can only see new ones).

The spacing of the roof joists was also 400mm (chosen deliberately) so that each one could meet a rafter. Note that this is a slightly non typical way of doing it. In many cases you would simply stick a steel in under the ridge to pick up all the rafters. We did not need to do this however because I was making two rooms that were to have a dividing wall not far from the ridge position. Hence the dividing wall actually takes the load of the ridge using the ends of the flat roof joists in cantileaver.

The size of beam required for the roof joist was calculated in Superbeam using a uniform loading due to the flat roof of 0.6kN/m (warm deck with three layers of hot bonded felt - so not that heavy). And a further point load of 0.48kN per joist exerted by the front roof rafter on the end of each flat roof joist at a distance of 0.8m from the supporting wall.

So looking at the side :

0.47 | Point load v _________________0.6kN / m__________________ / \ Uniform load

############################################## ############################################## ############################################## | | v v 0.67kN downforce on 2.21kN downforce on read dormer wall partition wall

Like the third one down?:

i plan on screwing or bolting and gluing together a 150*50 timber to

Note that your rafters are already comparable to my 4x2" rafters and are not as thin and skimpy as the matchstick wood they seem to make some trusses from. Hence I would expect if you stick a dwarf wall where the short arm of the W is, and a steel beam under the ridge, you may need no further strengthening of the rafters.

;-)