Roof timbers

[John]

In preparation for putting a boiler in my loft I am wondering if a particular timber is just what the builders used temporarily to support the roofing timbers whilst building the house. The house has what I believe is called a double hipped roof. The timber in question is about 3/4" x 3" - it runs at a shallow angle from the bottom of a roof member - upward to tie in with 3 others. Anyone able to advise? Do builders use temporary bits of wood to hold things upright whilst assembling the roof?

[John]

Maybe this link will work and clarify what I am trying to explain:

[Tim Watts]

that diagonal in are capable of resisting major shearing forces. So I

*think* that you are right and it was a building aid rather than an integral part of the structure.

Why is there such a large gap between those middle rafters? Without seeing the rest of the roof, what is there about the construction that would resist the roof folding flat, if that diagonal were important?

If you are concerned, you could screw that timber across the bottoms of the rafters right next to the braces and put in several short diagonal braces between the braces so they are not so obstructive which should add general stiffness to the assembly.

Some more photos of the rest of the roof could be useful.

[John Rumm]

It looks like a roof made from prefab trusses:

these it is indeed quite common to slap a strut across a number of trusses to hold em in place when assembling the roof. Doing it at an angle resists the ability of them to "rack" as a whole and move from the vertical.

If yours is hipped in construction, then there will be slopes at all sides and these will usually resist any lateral movement of the roof as a whole. Hence there is a fair chance that the timber is no longer fundamental. However don't take that as gospel since we can't see most of it, and this is just educated guesswork.

[John]

Tim - I have added some more photos - some looking up at the short ridge. The large gap aligns with the loft hatch and ceiling support timbers. There are 5 timbers supporting the ridge.

[John]

Additional photos added.

[Kipper at sea]

They are not temporary supports; they are all part of the stress of side movement on truss roof construction. It was found that in the early days of truss roof use, that when the weight of the roof tiles was loaded the trusses would sway. The diagonal braces, as they are called. Were introduced to stop sway. If you=92ve ever work on a truss roof without bracing, as you moved about it was a bit unstable. They are not put into position until all the trusses have been erected.

[John Rumm]

it - it does not tell us much more. The diagonal timber could be "moved" in the sense that a duplicate one could be fixed to the underside of the rafters (on both opposing roof slopes to be sure!) rather than the inner part of the W, and then the original one removed.

Why do you want to move it?

[John]

To make room for a panel on which to mount a combi boiler. I am planning on erecting a vertical timber to align with an existing vertical - then spanning the gap with a plywood panel clad in plasterboard. The space is above an existing boiler and on the same line as an existing flue.

[Tim Watts]

I'll go with that too.

The diagonal doesn't look very structural - not with that random bit of metal band on the base of it.

But, as John says, you cannot go wrong with some diagonals under the and across the rafters and the net effect will be the same - they'll be out teh way then.

I would use screws rather than nails to avoid banging the crap out of the roof (5mm ScrewTite or Reissers would make it simple without much risk of spliiting the rafters)

[Tim Watts]

Any reason they didn't strap the rafters with diagonals?

In fact. I have seen under-rafter strapping on my old rented house (modern truss roof) - so I'm *guessing* it was down to how the builders felt on the day?

[Hugo Nebula]

From the photos, I would have a few observations:

1. The centres of the trusses looks very random. Either the centres of the trusses either side are much less than 600mm, or the central pair are way over.
2. Just looked it up, and provided that the hips are properly constructed, and the distance between then is 1.8mm or less[*], you don't need diagonal bracing (under the rafters from wallplate to ridge) ...
3. Which you don't appear to have.

The bits of timber in question could be chevron bracing, but this is only required to trusses exceeding 8m in length[*].

You could move the chevron brace to run in an opposite direction, but I would be reluctant to remove it entirely without knowing for sure whether it's needed or not.

The other question is, "do you really want your boiler in the loft?"

[*] Assuming normal wind loads (i.e., you're not on top of a hillside or an exposed fen or something).

[John]

Many thanks.

The reason for planning to put the boiler in the loft is that I have very little built in cupboard space. The existing floor standing boiler occupies a substantial part of what could be a useful cupboard on the landing. To replace it with a wall mounted boiler would still require a significant amount of space being taken up - and the construction is only plasterboard (no timber supports) - whilst I could overcome any weaknesses, it seems that it may as well go in the loft - after all, it hardly needs to be accessed frequently.

I have looked at the timbers again and have decided that if I bring my proposed back board supports forward by 2" then I won't get a clash with the brace which was my concern.

The large spacing incidentally is 650mm (centre to centre)

[Andrew Gabriel]

They work best on the timbers which are nearest to being vertical. The rafters usually are the least vertical in a trussed roof.

[John Rumm]

Indeed, although many truss designs don't really have anything that is vertical - with bracing timbers often at the same angle as the rafter angle.