Shed walls starting to crack vertically

[b21playa]

Hi all

A few years ago I built a 6mx5m shed out of 150mm concrete blocks with a pitched roof at 25deg using concrete tiles and rendered it.

I have noticed on the back wall there is a crack either side on the outside forming top to about midway. From what I can tell it seem the weight of the roof is spreading which is causing the outer walls to move slightly.

I have no ceiling joists on the wall plates, but put in collars, a foor or so down from the ridge

What could I do to remedy this?

 

[luisdesign]

What did you use as foundations for the shed?

 

[b21playa]

What did you use as foundations for the shed?

Strip footings dug 800mm deep, 18" wide with 300mm depth of concrete.

Doesn't seem to be any movement in footings, and crack has started from the top

 

[stuart45]

The collars should be in the bottom third of the roof.

 

[b21playa]

The collars should be in the bottom third of the roof.

Maybe this is what is causing the issue

Would 4x2 be ok?

Would 3.6m lengths of timber ensure I'm in the bottom third, or should I go for 4.8m?

 

[stuart45]

4x2 is fine, although it's probably better to bolt them to the rafters.
Not sure on the length, but you can measure across.

 

[b21playa]

4x2 is fine, although it's probably better to bolt them to the rafters.
Not sure on the length, but you can measure across.

Would screwing them not be sufficient?

 

[noseall]

You have built a 6m x 5m shed with a pitched roof and no restraining joists?

FEKKINELL!

Collars a foot down from the ridge will be next to useless
Get some acros under the ridge quick.

 

[stuart45]

Would screwing them not be sufficient?[/quote]
Screws clamp wood together well, but don't have the shear strength of nails. The roof is pushing the rafters away from the collars.
Nuts and bolts clamp the timbers together and also have better shear strength than nails or screws as they are thicker.
The cost is not that much more.

 

[b21playa]

I'll get an acro under on weekend and support it

Would it be wise to extend the acro to push the ridge up, just incase it has dropped?

Will also go and get some bolts as well and fasten them. Hopefully I can save it in time

Edit

How about these bolts in 110mm or 130mm. M6 or m8? I guess it would need washer on nut end as well

http://www.toolstation.com/m/part.html?p=23047

 

[b21playa]

Managed to borrow some acros for the weekend, so I'll get wood ordered as well and hopefully get it all sorted weekend

Edit: got acros today so will get the roof supported this evening.

 

[Deluks]

M10s would be more suitable, square washer on the nut side.

 

[b21playa]

M10s would be more suitable, square washer on the nut side.

Thanks

Where can I get m10 square washers from? They all seem to be m12, so had to buy them.

I've got 50x100mm 4.8m lengths of timber on order for saturday delivery.

I also have some heavy duty L brackets (flat restraint stap bent halfway). Is it worth fixings these to the corners to help stop cracks increasing?

 

[^woody^]

Have you actually gone around with a long level to check that these walls are out of plumb?

Lateral (sideways) thrust from a roof tends to show as horizontal cracks not vertical. The bond of the wall prevents vertical cracks, and for 6" concrete blocks to crack vertically is very unusual for anything except foundation movement

BTW, if you are installing tie joists at that length, they will need one or two binders and maybe timber hangers dropped from the rafters

 

[JohnD]

I presume these vertical cracks are in the gable end walls?