Skewed roof structure

[shares]

Hello everyone, I would like some advice.

 

A couple of weeks ago, the carpenters who are building my roof, made a mistake and set a large part of the rafters at the right hand side lower than the left hand side by about 30-40mm. They cut really large bird mouths as seen on the photo.

 

Eventually they accepted it was wrong and they stripped it out and reset it with new timbers and proper birds mouths. Now at least my fascias and soffits will be at the same level, left and right side of the house.

 

However I have now noticed that the new rafters are now skewed to the right. That means that the rafters do not meet the ridge or the wall plate at right angles. I was told this is because they followed the right hand side wall (a gable wall) which is "off".

 

Thinking practically, once it is tiled and the inside boarded with plasterboard, I will not see the rafters anymore.

 

But can there be other implications I am missing? And should I ask them to strip it all out again?

[Mr Punter]

I don't think it will do any harm.  There is a fair gap between the insulation and blockwork.  Can you close this off at the top?

[Simplysimon]

birdsmouth 1/3 depth of rafter so no excuse for the first 'mistake', when you say the rafters are skewed, by how much? it's not ideal but if it's the amount in the top pic and only the bottom half which seems skewed it should be ok. ideally the rafters should be at 90deg and the last one place with less than centers between it and angled wall. 

i suppose the only upside with the build methods down south not having a roof board covering means centres don't need to hit sheet sizes unless room in roof

[saveasteading]

Very few buildings are at right angles. It's ok.

[shares]

   

1 hour ago, Mr Punter said:

I don't think it will do any harm.  There is a fair gap between the insulation and blockwork.  Can you close this off at the top?

That is YET another problem you have spotted there. There is a normal 100mm cavity wall, followed by an older style 50mm cavity wall. But in reality the cavity is 140mm and 90mm at the top couple of courses. Those bricklayers... 

 

1 hour ago, Simplysimon said:

birdsmouth 1/3 depth of rafter so no excuse for the first 'mistake',

Yes I know!

 

I do not know how badly the rafters are skewed by, but it is visible as you can see. I do not think they have nailed in all the tops yet, as you can see on the photo, I will have a more definitive picture may be tomorrow.

 

 

2 hours ago, Simplysimon said:

ideally the rafters should be at 90deg and the last one place with less than centers between it and angled wall. 

Exactly!

 

 

[ProDave]

2 hours ago, Mr Punter said:

I don't think it will do any harm.  There is a fair gap between the insulation and blockwork.  Can you close this off at the top?

I was going to mention that.  Unless you do some serious detailing before the top of that wall becomes inaccessible, then those slabs of insulation might as well not be there as the cold air will just completely bypass them.

 

Is there a plan to sort out that detail?  If not tell the builders to stop, not to cover the top of that wall until there is a plan.

[shares]

OK now I get it, the insulation must be firmly attached to the inner skin, and in places it is not. So we need to stick it on as best as we can before we lose easy access to it from the top. I believe it is just the very top course, as they were working off of trestles. I will go around and check tomorrow.

[ProDave]

4 minutes ago, shares said:

OK now I get it, the insulation must be firmly attached to the inner skin, and in places it is not. So we need to stick it on as best as we can before we lose easy access to it from the top. I believe it is just the very top course, as they were working off of trestles. I will go around and check tomorrow.

At a very minimum go around with a can of squirty foam and fill the gap between the blocks and the top of the insulation ALL the way around the building.

 

It is this sort of detail that most builders seem completely oblivious to.

[shares]

 

Can I lodge smaller chunks of insulation here and there to "push" the main insulation firmly against the blocks right at the top where there are no wall ties and retainers?

 

3 minutes ago, ProDave said:

It is this sort of detail that most builders seem completely oblivious to.

 

I am the builder as in I hire the trades in, but have not got a professional supervisor. Trades most often do not care about anything that goes on around them.

[saveasteading]

1 hour ago, shares said:

to "push" the main insulation firmly against the block

There are wall ties with spacers, so it should push back. But there seems to be a change in block line or thickness, where the insulation starts to bridge the difference.

Prob too late to change at your own expense, so ProDave suggestion prevails.  But see if you can push the slabs back and fix with the red spacers first.

[shares]

6 hours ago, saveasteading said:

But there seems to be a change in block line or thickness, where the insulation starts to bridge the difference.

In that photo, there is a 300mm cavity wall which becomes 250mm cavity wall.

 

There is 50mm cavity insulation followed by 25mm insulation where the cavity gets narrower.

[saveasteading]

And they have lined the insulation face up, rather than push it back to the wall?

[shares]

I am not sure I follow. It looks like this. Is something missing?

[shares]

OK I was just there and I can see whats happening.

 

 

[carlb40]

I try to square the joists up as much as possible. I usually take measurements from both the longest walls and ridge beam and try to square off those, so that any boarding is square to the joists. Then if the gable is out i can just add an extra joist to catch ply/ plasterboards etc. The last big roof i worked on was about 30 mtrs  long and the main roof was put on by people who didn't know what they were doing. The ridge beam was out of level by about 70 or 80 mm i think, which caused the rafters ( metal web joists) to protrude past the inner wall too much at one end causing me an issue with the box gutter. Because the joists were not squared up properly too when installed, every sheet of ply on the roof had to be cut to suit each joist.  

[shares]

On 17/02/2022 at 12:27, carlb40 said:

I try to square the joists up as much as possible. I usually take measurements from both the longest walls and ridge beam and try to square off those, so that any boarding is square to the joists. Then if the gable is out i can just add an extra joist to catch ply/ plasterboards etc. The last big roof i worked on was about 30 mtrs  long and the main roof was put on by people who didn't know what they were doing. The ridge beam was out of level by about 70 or 80 mm i think, which caused the rafters ( metal web joists) to protrude past the inner wall too much at one end causing me an issue with the box gutter. Because the joists were not squared up properly too when installed, every sheet of ply on the roof had to be cut to suit each joist.  

Thanks. Now they have torn down and re-made this section, a bit more square this time.