Building/roofing question

[Globs]

Hi Folks,

I'm building a hipped roof that meets an external house wall much like the one in this picture:



I'm referring to the roof on the right (mine has a hip though, but it's the same deal where it meets the house - closest pic I could find.).

On my roof plans, where this meets the house the truss maker has just left a c.25mm gap between the truss and the wall, so I'm not sure whether to bolt it straight to the wall, bolt it via some other wood or leave it free-standing(!?).

So before I bug the truss maker & building inspector has anyone done this before? - and if so how did you fix the truss to the wall?. The wall it needs to attach to is brick with cavity.

Thanks in advance!

[ShredderXLE]

You would normally leave a 25mm to 50mm gap between the rafters and the wall. The trusses are then fitted with horizontal galvanised steel restraint straps which are fixed back to the masonry wall and accross a minimum of the three and the void is filled with a packing / blocking piece where the strap is - and between the rafters.

I will see if I can dig out a picture to explain it.

See pages 20 - 21 of this guide as it shows the gap.

http://www.nhbc.co.uk/NHBCpublications/LiteratureL...

Obviously you cannot fit the straps in to the cavity on an existing building so you may wish to speak to your truss designer about some other similar brackets or bolt fixings.

Edited by ShredderXLE on Tuesday 29th March 22:49

[Globs]

ShredderXLE said:

You would normally leave a 25mm to 50mm gap between the rafters and the wall. The trusses are then fitted with horizontal galvanised steel restraint straps which are fixed back to the masonry wall and accross a minimum of the three and the void is filled with a packing / blocking piece where the strap is - and between the rafters.

I will see if I can dig out a picture to explain it.

See pages 20 - 21 of this guide as it shows the gap.

http://www.nhbc.co.uk/NHBCpublications/LiteratureL...

Obviously you cannot fit the straps in to the cavity on an existing building so you may wish to speak to your truss designer about some other similar brackets or bolt fixings.

Thanks for the link - will check it out.
I'm wondering if it would it still need restraint straps with a hip though? The hip is most of the roof then there is less than a metre of regular roof until it meets the wall.

[ShredderXLE]

I would definitely suggest that the new trusses are tied back to the existing wall in some way though, even if it is mostly hipped. You will also need to fit binders and bracing to the trusses - this is to prevent a racking effect so the first truss of the normal pitched part of the roof does need to be fixed back to the wall. Maybe the truss could be bolted through 50mm thick timber packing pieces ftted between truss and wall.

Also have a look at this guide for wind bracing etc

http://www.tra.org.uk/pdf_files/pds4.pdf

[Globs]

Yes I tend to agree, spacers may be the way to go. I'll see what the inspector suggests today. There is the gap (but no details) on the main plans too, and nothing in the notes.

The truss roof plan (that arrived with the trusses) has all the binders and braces specced out for the roof (inc loading for wind, snow, tiles etc) so that's nice and clear, it's just this little gap that's bugging me!!

I'll let you now what he says (next week if he wants to visit), he's the one inspecting it when it's done after all

[JR]

Globs said:

I'm wondering if it would it still need restraint straps with a hip though?

Yes; a hip is the least stable form of roof construction. The galvanised restraint straps are 5mm thk and won't buckle over a 25mm span so you don't need spacers but if it keeps the BCO happy...

[Globs]

Well I have the answer, space it 25mm from the wall with 3-4 wood pads with damp-proof between them and the wall. Screwing to the wall is optional, just through the pads if desired into rawl-plugs.

He seems to know his stuff TBH and was very definite about it. The gable on the house has for instance 5 x 5mm straps to anchor it into that roof, but not for the hip.

As far as I can see the hip cannot move because it's a trussed hip, so it has (3) triangles perpendicular to the wall (hip centre + jacks), anchored into the wall plate and the main (3-ply) hip truss, so I figure that's why (with the specced bracing) it doesn't need support to the wall.

The top of the wall it meets also has a hip on it (to smooth off the look of that side of the house) so besides the wall plates and hold-down straps there is no strapping there.

So I guess I'll use 4 pads (2 per side), some spare damp-proof and some 4" screws into blue 10mm hole rawlplugs.. giving a 1.5" (4 - 2.5) thread depth into the plugs.