Options for shed roof ties?

[Ivor Windybottom]

Hello. I'm currently about to build a brick shed - cavity walled, with clay brick outer and concrete brick inner. It won't be plastered or painted inside, the (light coloured) bricks will be the finished interior wall. It will have a flat roof, not sure yet whether it will or won't have a wallplate - I'm limited by the 2.5m permitted development height.

Obviously the roof needs strapping to the walls so it doesn't blow off. The ties I've seen before screw into the interior surface of the interior wall then get buried within the plaster. I suppose this could be an option for my shed but it would be a bit ugly, as it won't be plastered.

Are there options for invisibly strapping the roof down? The best idea I can come up with is to built the inner skin first then fix the straps onto the cavity side of the wall before building the outer.

What's normally done in buildings that won't get plastered?

 

[Ivor Windybottom]

To clarify, this is what's normally done...

I'm thinking of putting that strap inside the cavity. But this could be awkward.

Altnernatively, is there some kind of system to do this without drilling and screwing? I'm thinking perhaps some special wall ties you could build in a few courses down, then hook some sort of vertical rod onto after.

 

[George_engineer]

Usually they're just left on show - if it's a blockwork finish, aesthetics clearly aren't at the top of the list!

You could bolt the wall plate/rafters to the blockwork.

For a wall plate this can be a simple frame fixing or resin anchor. For a rafter this would need to be via a angle bracket.

You would need to increase the number of fixings compared to a holding down tie - this is because the fixing would only connect to the top course of blocks, where as the ties engage ~3 courses of blocks. On a simplistic analysis you would need x3 number of fixings, or a 600mm nominal centres (i.e. one per rafter). I would be more comfortable with a wall plate in this arrangement but an additional line of noggins at the wall would mitigate the lack of a wall plate.

 

[Ivor Windybottom]

Thanks for all the info, much appreciated.

The inner wall will be brick, not block. I know this is a bit unusual these days, I'm just wanting a hard-wearing surface that doesn't need painting and found some light coloured fairly smooth bricks going for a good price. So bolting to the top would anchor it to a 2kg brick only. So it definitely needs a strap of some sort, to attach it lower down and have some weight above the fixings.

It's just a shed, but I was hoping to make it a bit posher than average. Surely not all bare brick/block buildings have metal straps all round the room?

Is there a reason why I couldn't build up the inside first, then attach some of those twisted straps shown, then build the outer wall? I'd probably just fix into the mortar rather than the bricks, as it would be only a day or two old when drilling so would fall apart if I drilled the bricks.

I'm surprised if nobody's invented some kind of build-in system, e.g. some sort of heavy wall tie you can later hook a strap onto.

 

[Ivor Windybottom]

Here's a potentially mad idea - could I just build these into the bricks? I've rotated the picture to show my intended way up, the vertical part would be inside the cavity...

Heavy Duty Restraint Strap 1000mm Bent 100mm Twisted 100mm

Galvanised Heavy Duty Restraint Strap 1000mm Bent 100mm Twisted 100mm is designed for lateral and horizontal restraint (as in roof trusses). The straps are produced from edge coated galvanised mild steel, also available in stainless steel. They are designed for 6mm and 25mm offse

www.buildersmetalwork.com

It's 900mm long, so if that bent bit is built in 10 courses down from the top then it would end up sticking up by 150mm above the wall top. It would need some careful placement to align with where the joists will go. They weigh 930g, so hopefully one brick and its kilo of mortar should hold it up on its own just by gravity before the rest are put on top of it.

Perhaps shorter would be better, if they exist elsewhere.

The bent bit is 100mm, but won't go all the way in due to the twist against the wall face. So it should be just under the pointing on the inside.

I might buy one to try building one in as an experiment while building the foundation courses, see if it's totally impossible.

 

[^woody^]

There are thousands of flat-roofed sheds, garages and other buildings that do not have straps, yet still have roofs after decades.

 

[George_engineer]

There are thousands of flat-roofed sheds, garages and other buildings that do not have straps, yet still have roofs after decades.

Hmmm.. there's a fair few roofs that get blown off too. It would depend on location, exposure etc etc. The uplift forces shouldn't be underestimated.


You can safely build the innerleaf up (NHBC says 6 block courses - which sounds bit much to me, and wouldn't overdo it with brick - more usual to see 3 block courses ahead), giving you plenty of room to fit the holding straps into the cavity in the normal way.

 

[noseall]

You can safely build the innerleaf up (NHBC says 6 block courses - which sounds bit much to me, and wouldn't overdo it with brick - more usual to see 3 block courses ahead), giving you plenty of room to fit the holding straps into the cavity in the normal way.

We usually get small extension blockwork, up to lintel height in a day, lol.

 

[Ivor Windybottom]

There are thousands of flat-roofed sheds, garages and other buildings that do not have straps, yet still have roofs after decades.

It will be in a very open area, and I don't want to take a gamble. It does happen. I also have a 30-year old flat-roofed room which has an insufficient number of ties and it does make a few movement noises when it gets windy, and there is a hairline crack all around the wall/ceiling joint.

Those ones with an angle and a twist shown above are pretty special. But I'm going to buy an angled only one from Toolstation to play with while I'm building the foundation courses, if a brick is capable of holding one in place before more are built on top then I'm going to buy those shown and build them in. There's no way anything could ever move if the joists are screwed to a tie that's built into the brickwork.

 

[^woody^]

Here's a potentially mad idea - could I just build these into the bricks? I've rotated the picture to show my intended way up, the vertical part would be inside the cavity...

View attachment 307558

Heavy Duty Restraint Strap 1000mm Bent 100mm Twisted 100mm

Galvanised Heavy Duty Restraint Strap 1000mm Bent 100mm Twisted 100mm is designed for lateral and horizontal restraint (as in roof trusses). The straps are produced from edge coated galvanised mild steel, also available in stainless steel. They are designed for 6mm and 25mm offse

www.buildersmetalwork.com

It's 900mm long, so if that bent bit is built in 10 courses down from the top then it would end up sticking up by 150mm above the wall top. It would need some careful placement to align with where the joists will go. They weigh 930g, so hopefully one brick and its kilo of mortar should hold it up on its own just by gravity before the rest are put on top of it.

Perhaps shorter would be better, if they exist elsewhere.

The bent bit is 100mm, but won't go all the way in due to the twist against the wall face. So it should be just under the pointing on the inside.

I might buy one to try building one in as an experiment while building the foundation courses, see if it's totally impossible.

That would work.

However, get the medium duty or 2.5mm straps, as these are easier to bend/adapt.

You'll need to cut the angle part that will go into the joint, as these are normally more than 100mm. Paint any cut ends.

Or just get flat straps and bend to suit.

These would need to be built in at least 9 course/675mm down from the top. Bang a nail in at the subsequent bed joints.

 

[Ivor Windybottom]

Thanks for the reassurance, I know I'm being a bit unusual with this. There is what they call light duty. These in fact...

Light Duty Restraint Strap 1000mm Bent 100mm Twisted 100mm

Galvanised Light Duty Restraint Strap 1000mm Bent 100mm Twisted 100mm is designed for vertical restraint, for example fixing wall plates to masonry and also for horizontal restraint. The straps are produced from edge coated galvanised mild steel, also available in stainless steel

www.buildersmetalwork.com

This is 2.4mm. The shed is small and will have dozens of these, so they should be easily adequate. They only weigh 508g so hopefully won't topple about before the courses above are in. £2.40 each sounds good too!

These have a 100mm bent bit, so roughly equal to a brick width. But I'll need to leave it not quite full inserted to make space for the twist above, so probably only inserted about 80-90mm, so no cutting therefore the coating will remain intact and will be below the pointing so hopefully no rust stain in a few years.

As a test, I'm getting an untwisted near equivalent from Toolstation today (1000mm, light duty, bent but no twist). When I'm building the foundation courses next week I'll try building one in to see just how annoying it is. I'll jut it out slightly, pretending there's a twist to make space for.

I'll be using fibre cavity insulation, so it should bend and stretch around them OK.

 

[Ivor Windybottom]

These would need to be built in at least 9 course/675mm down from the top. Bang a nail in at the subsequent bed joints.

Sounds like a wise precaution to give extra support, I might just push a woodscrew into the wet mortar as I go.

 

[Mr Chibs]

What about just putting something really heavy on the roof.

I'll get my coat!

Joking aside, why can't you build up half way, then build the inner course to final height, fitting ties, wall plate, and use normal restraints on (fitted on the reverse of the inner course)
Then finish the remaining outer course of brick/block.

 

[Ivor Windybottom]

What about just putting something really heavy on the roof.

I'll get my coat!

Joking aside, why can't you build up half way, then build the inner course to final height, fitting ties, wall plate, and use normal restraints on (fitted on the reverse of the inner course)
Then finish the remaining outer course of brick/block.

That's what I was thinking at first. Then I started thinking that it would involve hammer-drilling into a single skin of brick that had been built the day before so I could have ended up with a pile of rubble on the ground.

Which is why I'm now thinking of doing it using something that can be built in from the start. Hopefully, depending on how much of a pain in the arse it is having a 1m long bracket sticking up out of the wall that might just want to fall over. That's why I'm buying something similar to play with while building the lower courses, to see just how stupid this idea is.

 

[Mr Chibs]

Just drill it without hammer action.

If you use those brackets illustrated upside down, the small bit in the brickwork you won't be able to fix the length of it to the wall...just the wall plate/rafter.

I see what you are thinking though.