Strengthen a half brick wall on a 7m x 4m building

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Hi all,
Im after some advice. Ive built a summerhouse last year using 100mm building blocks then cladded with shiplap. The building is 7m by 4m and 2.5m to the eves with a pitched roof.

I am now reading that 100mm wide blocks are not suitable for structural/load bearing walls and so am wanting to put some piers in, especially along the 7m sides. I was thinking to put a 4x4inch fencepost on the inside of the wall to brace it if the wall does decide to crack in future. Then I was going to sink some fenceposts into the ground on the outside to lighten the load of the roof. This seems like a bit of a bodge fix though and im sure I should of put in some piers. Is there a way these can be added afterwards?

To make the situation more akward the building has a substructure which involves a 50cm tall tanking wall (building blocks laid on their sides) then at ground level it goes into the single skin/ half brick wall all the way to the eves. 2 blocks before the eves I added mortar joist hangers and created a small upstairs room/attic. My fix was going to be running a few fence posts from the foundations upto underneath these joists and then somehow fixing the post into the wall. If need be I shall strip back the plasterboard and add a pier on the inside or strip back the cladding and add a pier on the outside but im hoping thats not nessacary.

I spoke to a builder who reckoned it should be fine as it gains strength from the corners of the building but I read that I should have piers every 3m.

This is meant to be used as a family garden room and playhouse for my son so am concerned about safety of course.

Any advice is greatly appreciated
 
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It is also worth mentioning there is another wall built with 100mm thick blocks inside the building and tied into the 4m side wall. This wall is about 6m long. The roof is tiled with tapco plastic tiles to decrease the amount of weight bearing on the wall.
 
The vertical weight on the blockwork may not be that much of an issue. What is more important is lateral stability under wind load, and on a 7m run 2.5m high, that does need something doing.
Hard to say from your description - there will be several ways of achieving stiffness - a few pics and/or simple sketch plan would help.
 
I have attached a few random pics from what I had available on this pc. As you can see the joists start 1.8metres up the wall so although the wall is 2.5metres it is supported 1.8m up. Another person I spoke to mentioned wind also. I was building it during last winter and we had some pretty hectic weather which it seems to have survived through but maybe I was just lucky. Do you think the fence post method would work based on the pics?
 

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You wont need piers for a building of that size. Its all braced from the corners as your builder says, plus the internal walls plus the roof.

Suitable roof construction would be a more significant factor than the wall construction.
 
Thanks for the reply woody, that certainly puts my mind at rest. The thing about piers every 3metres still makes me want to put a fence post on the inside middle of the 7metre walls. Ive attached some piccys of the roof
 

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Where did you read about piers every 3m?

That doesn't apply to buildings, it applies to straight flat walls (such as tall garden walls) that might otherwise blow over.

I don't know much about roofs, but I can't see what prevents your pitched roof from spreading and pushing the tops of the walls off.
 
If that floor is well-fixed to the long wall and the 4m-end walls, you should be OK for wind load, as the floor acts as a rigid plate and transfers load to the end walls.
Are you in Scotland, by chance?
 
Yep the floor joists are fixed into the wall using mortar joist hangers, noggins between the joists also. The roof uses an attic style truss each end with 2 extra supporting posts in the middle. The wall plate is bolted down to the wall also. The tiles are lightweight plastic to minimise the weight of the roof. The floor isnt fixed to the 4 metre walls but a partition wall within the building is tied into one of the 4m walls, the other end of this wall has a lintel for a doorway tieing it into the other 4m wall. Imagine the building having 2 long rooms, one that is 2.4m wide and 7metres long. The other being 1.5metres wide and 7metres long.

Nope not in scotland, im in Oxfordshire. I did plan on building a veranda out the front at some stage and wondered whether a small stone wall in front of the building would act as a wind block to some degree. I was also thinking of sinking some posts into the ground to support the roof to avoid it spreading like you say. This would have a double use for the porch/veranda.
 
I read about piers every 3m from another post on here but your right it could have been for a garden wall. The building has been stood for over a year now with no issues and went through the winter wind rain and snow just as bare walls with no roof. I guess with it being such an odd design I thought id get some other opinions.
 

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