Building inspection - roof structure not as per plan

[GCarnegi]

Hi all,
Just had my building inspector round this morning to check my extension against the completion certificate.

He found a couple of minor issues, but potentially the most major one is that my joiner has built the roof with 225 timber at 600 centers instead of 250 timber at 400 centers. Also, the hip rafters are singles, where "doubles" were requested on the plans, apparently - though I don't think the hip rafters themselves see much load, as they are supported by the jack rafters, so not sure that this is so much a big deal.

Of course the extension is "finished" now, with the roof fully slated (costing £12,000) and the rooms below are ready to move into, plastered, painted, carpeted and fitted wardrobes installed.

The inspector has asked for an engineer to look at the build and approve that the structure is sound.

Is this something I should be doing myself, or should I get my joiner to sort out the engineer, and any relevant rework?

thanks
Guy

 

[big-all]

minor issue
225 at 600 is probably close to doubling the load over 250 at 400 centers so hardly minor unless way over specked in the first place

 

[freddiemercurystwin]

Why did he not build it as per the drawings? Did he have the drawings? Did he discuss any of this with you. Did you employ him or did you have a builder employ him? ?Have you paid him?

If the BCO has a drawing that's been approved then any deviation will warrant further investigation especially structure. That said 250mm rafters at 400 centres are huge! And double hip rafters is unusual. What are the spans etc you'll have to elaborate a bit more if you want advice on timber sizes. Who did the drawings an architect not an SE presumably? Sounds like he oversized everything to me to cover himself!

 

[GCarnegi]

*double post

 

[GCarnegi]

Inspector says there should be a double hip rafter, though i couldn't make that out on the plans - guess the joiner couldn't either. Length of the hip is approx 7m, so has been scarfed near the bottom end.

I'm certain the SE has massively overspecified the structure, as the joiner did say that the way he did it was how it is "normally" done. Of course, getting the SE to admit he has done so might not be easy. Maybe I should go with another SE for the check.

I remember when the joiner brought in the timber for the roof, I noticed it was 225 instead of 250, and I asked the SE if this was okay, he did some calcs and said it would still be okay. No mention was made my me of the 600 centres though (I didn't realise until now that it wasn't as per plans).

Roof pitch is 43 degrees, and max horizontal span is about 4m (ridge to wall).

Joiner is all paid, and is very friendly and reasonable. He was brought on-board by my builder, but all financial transactions have been direct with me.

 

[catlad]

I can not see why you have a 7m hip, but anyway I would agree with your joiner.

 

[datarebal]

7mtr hip means rafter length not unusually long, 225 not unusual 600 c is crap especially if your the slater.
saving grace I reckon is it's a slate roof so not overly heavy.. balls in SE court i'd say..

Mind you, how come BCO took all this time to mention timber sizes?

 

[GCarnegi]

When I submitted the plans to the BCO this time last year, I asked him which stages he would like to come down and see the progress.
He told me just to give him a call when everything is finished - hence why just spotting build just now. Maybe I should have insisted?

When you say 600 ctrs are crap for the slater - he was indeed siptting feathers while he was working, and called the joiner all sorts!

When you say you agree with the joiner, do you agree he was right to deviate from the plans without discusing it with BCO at the time of the build?

Do we think that a mistake has been made somewhere? If so, who should rightly pay to investigate and rectify it? If we agree it (maybe) wasn't my mistake, then would it be proper to put the joiner in touch with the BCO and the SE, and ask that they sort it out between them?


I'm open to suggestions that it might be me who made the mistake by not checking my joiners work, if that's what the concensus is. That said, are all customers responsible for checking professionals work, including the little old lady type?

 

[datarebal]

All the BCO is after is the SE to say it's ok... his first calcs may have been ott but we dont know that for sure.. I have to admit 250 mm rafters are few and far between....

who ever made the decision to deviate from the spec,,should really carry the can.

I still think the BCO should have inspected roof timbers, insulation, etc before plastrboarding. a bit naughty i think.

 

[GCarnegi]

TBH I reallly don't think the SE paid all that much attention to my build.

I had an existing hip which was moved "outwards" by approx 5.5m.

SE had apparently "designed" the old roof to be completely removed (not easy on a end-terrace - while we are still living inside), and a new roof built from scratch ove rthe whole house. Of course, there are existing dormers etc which this would have affected [or destroyed!] which would make all bedrooms in the house ununhabitable for the duration of the build.

Joiner apparently spoke to BCO for advice and was told he could simply put a "lay" rafter onto the old hip, and build off that.

Rafters on old house are only 150mm (or 6" as it's a 1940's granite & slate job), and that's been solid as a rock for the last 60 or 70 years, so I'm not sure why we need 250mm rafters to support essentially the same roof, exstended outwards.

So essentially it looks like there were a few mistakes made by:

SE: Should have designed the roof in the first place to use a lay rafter and to properly address the specific loads of the property.

Joiner: Should have queried plans with SE, and confirmed any deviations before jumping to conclusions. Should have spoke to BCO about changes before being made.

BCO: Should have inspected the build at more regular stages.

Me: Should have shimmied up the scaffolding to measure everything after joiner did it. Is it morally right that the customer should be the one to pay for the mistakes of these engineers?

 

[theoldun]

Interesting post, therefore for what they are worth, will give you our thoughts.
Starting from the back end. In all our years we have only known of one minor mistake by a SE. Unless your SE is a fly by night, he has a reputation and PI to consider and it is in his own interest to ensure that his drawings and calculations are correct. We have found that in the last 5 to 10 years SEs have increased their safety factor considerably.
Next, if the carpenter had been employed and paid by your builder and the roof timbers were at the wrong centres then you could have taken your builder to task, but as it would appear that you employed the carpenter direct on either a labour and material or labour only contract and he has not complied with the drawings then you have to take to task your carpenter.
You state that the carpenter is friendly and reasonable at present, but if he is just a normal subcontractor with very limited funds, you will likely find that his attitude will change once you put the big hammer on him and then you will be fighting a losing battle, unless of course you have a written contract with him? One of the joys of self management.
We feel that your BCO is being very reasonable for asking for a SE to prove the roof timbers as they are not correct to the drawing
From the sketchy information supplied, if the slope of the existing rafters are 4 metres at 43 degree pitch, then the depth of the extension is approx 3 metres from existing house to external wall of extension. If this is the case and the roof is slate with a loading of 0.41KN/m2, then SE should have no problem in proving that 47x225 is more than adequate, and will comply with TRADA span tables..
With regard to hip rafter, controversy has always surrounded this part of a roof and no tables are printed to calculate size of hip rafter. A note is always added hip rafter to be calculated by SE. When I was a lad I was taught the rule of thumb, increase hip rafter by quarter the thickness of commons, consequently we always make our hips 63x220, although saying that we have worked on numerous roofs with 50x200 hips. If your commons are approx 4 metres your hip should be approx 6400. You should not have a scarf joint on a hip unless joint is supported.
For what it is going to cost you, suggest you go back to SE. If he can not prove roof at 600 centres, then come back.
Hope this helps.
Regards oldun .

 

[tony1851]

This post raises the perennial problem of the hip rafter. I may have been away when we did them but I have never come across any structural calcs for hip rafters.
Contrary to what many inspectors seem to believe, they do not 'push out' at the corner; they are also propped by the rafters both sides. The depth of the hip seems to be a function of the depth of the rafters or purlins, rather than related to the span.

 

[Harbourwoodwork]

OK so how did it end then

 

[GCarnegi]

Waiting for letter to come through from inspector showing exactly what he wants.

 

[RonnyRaygun]

This post raises the perennial problem of the hip rafter. I may have been away when we did them but I have never come across any structural calcs for hip rafters.
Contrary to what many inspectors seem to believe, they do not 'push out' at the corner; they are also propped by the rafters both sides. The depth of the hip seems to be a function of the depth of the rafters or purlins, rather than related to the span.

It always upsets me when I am asked to design a hip rafter. "Design it like a rafter with a varying load" I've been told. Despite my protests that I don't believe that's what is actually happening, they always need to be double 200x50s minimum. Much bigger than any hip member I have seen in any attic I've been in.