Slumping garage roof

[CrispDust]

Hello all,

First post so I hope this i in the right section.

 

We have a detached garage that was built about 7-8 years ago. We purchased the property recently, after renting for some time.

The garage is about 12' wide by 20' length with a hipped roof. inner block leaf and an artificial "stone" outer.

We have noticed over the past few months that the top 2 or 3 courses of the block work on all 4 walls, to a varying degree, have started to tilt/bow outwards.

Most of the top course are at a noticable tilt and have seperated from the mortar.

There is obvious bowing of the soffit on the external walls.

I assume this has occurred due lateral thrust from the roof?  The roof is hipped construction. There are no horizontal joists.

On closer inspection I have noted the following issues which don't meet NHBC regs:

 

The wall plate does not have half lapped joints at the corners. There is notable seperation of the joints on 3 or the 4 corners.

There are no angle restraints/joists across the wallplate corners.

My understanding is that the wall plate acts as a strain ring to resist the lateral thrust.

There are only 2 vertical straps on each short wall, 3 on the longer wall. All at least 3 to 4m apart with 3 nails tapped into the mortar, not the blocks.

Do vertical restraints add to the thrust resistance from the roof or are they solely just as anti lift restraints?

 

The wall plate over the door simply sits on the metal lintel, no obvious fixings.

As mentioned previously, there are no horizontal joists between the joists, although I undestand this is usual for a hipped roof design?

There has been no loading on the roof from storage or hanging items tools etc.

 

Any comments before I get the original builder and original roofer round? Anything else I should be looking out for?

Thanks in advance.

[joe90]

10 minutes ago, CrispDust said:

There are no horizontal joists.

The very reason it’s falling apart. Any chance of a picture?

[PeterW]

14 minutes ago, CrispDust said:

My understanding is that the wall plate acts as a strain ring to resist the lateral thrust.

There are only 2 vertical straps on each short wall, 3 on the longer wall. All at least 3 to 4m apart with 3 nails tapped into the mortar, not the blocks.

Do vertical restraints add to the thrust resistance from the roof or are they solely just as anti lift restraints?

No no no ..!  That is incorrect !!! A wall plate is only there to provide a suitable fixing point for the roof structure. 
 

15 minutes ago, CrispDust said:

Any comments before I get the original builder and original roofer round? Anything else I should be looking out for?

Thanks in advance.

Yes - get a hard hat, get anything valuable out of it and then get signs up saying dangerous building on it !!

 

I would get your insurance company to look at this too - was this a new build and was the garage built under any sort of building regs .?

[markc]

Agree with Peter and joe on this one, sounds like it’s at failure point and a snowfall would bring it down.

as a temporary measure you could prop the ridge to stabilise it while emptying.

[joe90]

15 minutes ago, markc said:

you could prop the ridge to stabilise it while emptying.

?

1 hour ago, CrispDust said:

I get the original builder and original roofer round?

Please let us know what they say (if you can get them to come ?). Be prepared for B S .

[CrispDust]

Thanks for answers.

My son is an architectural tech but for commercial not domestic builds. He says a hipped roof doesn't normally have horizontal joists. I was surprised at this.

Here are some photos:

[epsilonGreedy]

1 hour ago, CrispDust said:

Any comments before I get the original builder and original roofer round? Anything else I should be looking out for?

 

 

Contact your conveyancing surveyor and ask him to visit to explain how he missed such manifest structural deficiencies.

 

What type of tiles do you have on the roof? I ask because with this information the weight of the roof can be estimated.

 

 

[epsilonGreedy]

4 minutes ago, CrispDust said:

Thanks for answers.

My son is an architectural tech but for commercial not domestic builds. He says a hipped roof doesn't normally have horizontal joists. I was surprised at this.

 

 

Buy him a book on roof structure design for Christmas because there is a gap in his knowledge.

[ProDave]

It looks like that was built as a vaulted roof hung from that ridge beam but that does not really work with a hipped roof without steels to support it at the end.

 

The solution is simple, a horizontal timber say 4 by 2 across the roof at wall plate height strapping  each rafter to it's neighbour the other side, securely bolted at the junctions.  this will stop the spread.  You might want to set up something like a Spanish Winch to pull the sides back into place at each rafter before bolting the cross members.

 

The purists will say roof off, re lay the cracked courses and rebuild the roof.

[joe90]

5 minutes ago, CrispDust said:

a hipped roof doesn't normally have horizontal joists.

Ah, hips do give some structural support, but yours ain’t,, my house roof was designed as hips without ties but the BCO insisted on vertical steels to the ridge at both ends , it would have taken to long to argue so we just did it. If you had “ceiling joists”, this would not have happened (and I have built many garage roofs, converting them from leaky flat ones!).

[CrispDust]

Ill get some info on the tiles.

The garage was built whilst we were renting.

 

So the bottom line is, the roofer (who was not linked to the builder) should have put some horizontal joists across the rafters?

[joe90]

Just now, CrispDust said:

should have put some horizontal joists across the rafters?

In my opinion, yes. (Whatever the tiles are).

[markc]

21 minutes ago, CrispDust said:

Thanks for answers.

My son is an architectural tech but for commercial not domestic builds. He says a hipped roof doesn't normally have horizontal joists. I was surprised at this.

Here are some photos:

Wether commercial or domestic, roof loads have to go somewhere, yes you can have hipped roofs without ties but then they need moment connections at the top.

unfortunately you have a low pitch roof, simple hip to ridge connections, weak walls and very little to hold the eaves together…. 
they could have used trussed or tied rafters and there would have been no problem

 

[CrispDust]

Looks like the roofer is in for a big bill.

[ToughButterCup]

2 hours ago, CrispDust said:

...

We have a detached garage that was built about 7-8 years ago. We purchased the property recently, after renting for some time.

The garage is about 12' wide by 20' length with a hipped roof. inner block leaf and an artificial "stone" outer.

We have noticed over the past few months that the top 2 or 3 courses of the block work on all 4 walls, to a varying degree, have started to tilt/bow outwards.

...

 

Just a thought, why has it taken (say) 6 full years to 'move' ?

Have you looked at the foundations? Might that (as well as poor workmanship higher up) be a contributory factor?  I ask, because if my suspicion  is right,  then sorting the foundation could well be as important as the other issues pointed out above.

 

And if I were a roofer, I'd want to argue that the foundations had moved, not the roof. So its worth a careful look at least.

[joe90]

3 minutes ago, ToughButterCup said:

And if I were a roofer, I'd want to argue that the foundations had moved, not the roof. So its worth a careful look at least.

Sorry, I disagree, unless there are cracks elsewhere which have not been mentioned ?

[Dave Jones]

bolt some collars on them. 

 

[CrispDust]

Re the 6 years delay to movement. I did wonder that myself. I am in and out of the gagrage almost on a daily basis as all my car tools/equipment, gardening stuff and woodworking tools, garden furniture/BBQ/pizza oven etc are kept in there and have never noticed the tilting blocks previously.

 

As an aside, I think my notion of a correctly constructed  wall plate being a strain ring has some merit?

 

[Adrian Walker]

4 hours ago, CrispDust said:

Hello all,

First post so I hope this i in the right section.

 

We have a detached garage that was built about 7-8 years ago. We purchased the property recently, after renting for some time.

The garage is about 12' wide by 20' length with a hipped roof. inner block leaf and an artificial "stone" outer.

We have noticed over the past few months that the top 2 or 3 courses of the block work on all 4 walls, to a varying degree, have started to tilt/bow outwards.

Most of the top course are at a noticable tilt and have seperated from the mortar.

There is obvious bowing of the soffit on the external walls.

I assume this has occurred due lateral thrust from the roof?  The roof is hipped construction. There are no horizontal joists.

On closer inspection I have noted the following issues which don't meet NHBC regs:

 

The wall plate does not have half lapped joints at the corners. There is notable seperation of the joints on 3 or the 4 corners.

There are no angle restraints/joists across the wallplate corners.

My understanding is that the wall plate acts as a strain ring to resist the lateral thrust.

There are only 2 vertical straps on each short wall, 3 on the longer wall. All at least 3 to 4m apart with 3 nails tapped into the mortar, not the blocks.

Do vertical restraints add to the thrust resistance from the roof or are they solely just as anti lift restraints?

 

The wall plate over the door simply sits on the metal lintel, no obvious fixings.

As mentioned previously, there are no horizontal joists between the joists, although I undestand this is usual for a hipped roof design?

There has been no loading on the roof from storage or hanging items tools etc.

 

Any comments before I get the original builder and original roofer round? Anything else I should be looking out for?

Thanks in advance.

 

You mentioned NHBC, so I guess there is a warranty with it?  In most cases NHBC warranties are very difficult to claim on, and as suggested I would go after the conveyancing surveyor.  The builder won't care, he has been paid.

[joe90]

31 minutes ago, Adrian Walker said:

You mentioned NHBC,

Not worth the paper it’s written on ! Try the surveyor but don’t hold your breath, they have get out clauses you never heard of. I would want to pull the wall plates back in line then bolt timbers across the roof, I prefer half way up to the ridge or below that if you can, you can always point  up the top row of blocks and wall plate. Oh and put more straps on screwed into the blocks.

Edited November 23, 2021 by joe90

[markc]

As an aside, I think my notion of a correctly constructed  wall plate being a strain ring has some merit? 

I agree, that does mean taking the roof off to do it as a wall plate.

you could jack up the ridge to correct height (plus a bit) and then add tension members (cables, flat bar etc) adjacent to the wall plate to hold the hips together.

[Conor]

2 hours ago, CrispDust said:

Re the 6 years delay to movement. I did wonder that myself. I am in and out of the gagrage almost on a daily basis as all my car tools/equipment, gardening stuff and woodworking tools, garden furniture/BBQ/pizza oven etc are kept in there and have never noticed the tilting blocks previously.

 

As an aside, I think my notion of a correctly constructed  wall plate being a strain ring has some merit?

 

Is it possible the movement had already happened but you didn't notice it?

 

As echoed above, you'd want to get some acrows in, jack up the ridge and stick some rafters in. A day's work. A few straps on the wall plate would be nice as well.

[epsilonGreedy]

2 hours ago, CrispDust said:

As an aside, I think my notion of a correctly constructed  wall plate being a strain ring has some merit?

 

 

Not really in the case of 4.2 timber wall plate along a 20ft wall. The wall plate and straps are there to stop the roof trying to lift off like a aircraft wing during storm force winds. A shallow pitch hipped roof creates more aerodynamic lift than a regular roof.

 

Have you checked how the rafter ends are fixed to the wall plate?

 

Re. a solution. As per others, jack the ridge up a bit and add some joists. The wall seems low, what ceiling height will result if the extra joists are fixed at wall plate height? If too low fix them higher as @joe90suggests, I'd suggest 1/3 of the way up towards ridge height.

 

Your structural ring notion has some merit at the 4 corners where the hip rafters meet the wall plate. Google for "NHBC hip rafter dragon tie". This should find a page showing designs for fixing the hip rafters to eliminate outwards slipping movement.

[joe90]

3 minutes ago, epsilonGreedy said:

 

Not really in the case of 4.2 timber wall plate along a 20ft wall.

+1

[saveasteading]

Pulling together all the good advice above....we would expect that the walls are buckling out most at the middle of the walls as the roof is restrained at the corner by the hip, and the walls there are restrained by the corner of the blockwork.

The cracks and movement being at the top suggest that it is only the roof and that the founds are ok.

 

I agree with the suggestions. more photos first, then jack up with a couple of acrow props under the ridge. Buy second hand if it will be for more than a few weeks. Best put a timber bearer on the floor if it is the same builder.

 

The NHBC warranty isn't often much help, the surveyor will have get-out clauses, the building inspector doesn't check everything, the builder probably doesn't have insurance worth anything to you. But try.

But do tell your insurer promptly or they will also say you took too long. They may pick the claim up and chase these others.

they will then allow you to get repairs done, and might even pay for  an Engineer.