Bow in Roof - How big could the problem be?

[dmills27]

Hi all,
I am looking at buying a new house and after settling on one I noticed that the roof has a bow in it the is quite noticeable. It looks like it has concrete tiles, and has had a loft conversion, I am no expert but would suspect that the rafters were not strengthened adequately when the conversion was done. Firstly does anybody know what sort of issues this could cause? secondly what kind of fix may be required, and is it a very big job? The house is ideal in other ways, and I would be prepared to pay up to 5k to fix the issue but if it is going to be a complete nightmare then I may have to walk away.

Thanks in advance.

 

[gregers]

im sure if there is a problem then your surveyor would pick the problem up?

 

[Ossy]

I assume the bow is noticeable along the ridge of the roof. This is most likely to be eaves spread caused by insufficient tying of the rafters at wall plate level, quite probably by the alteration of the roof truss arrangement/structure. Addition of a new heavier roof covering will have made it worse or just made it noticeable.

Patress plates and tie bars used to be a solution, but have proved over history to not be a lasting solution as the walls tend to bow out around the plates and only delay things.

Best solution is to tie the existing rafters at the wall plate level, but this might not fit in with the floor levels, and will not cure the bow in the roof, just prevent future movement. It would also be very difficult to do with the roof on.

To remove the bow will require the roof off. Installing a steel ridge beam and re-roofing - should prevent future movement and restore a nice straight roof line. Costs more than likely over you £5k budget.

If you're buying on a mortgage the surveyor should pick up the roof problems, and find out if building regs were submitted at the time of the loft conversion, then recommend a structural report.

 

[^woody^]

You don't say if this is a 1580 Tudor cottage - where roof dip is common, or a 2007 Barratt Home, where a dip is not so common.

In any case a roof dip with a loft conversion is not that unusual, but still of concern

What needs to be done is determine if there are signs of progressive movement, or if the roof has sagged a while ago and the stopped.

There is no need to try and restore it, only stop it going further if that is what is occurring

You need to spend £300 now on a proper appraisal rather than £10k later

 

[Shytalkz]

...or a 2007 Barratt Home, where a dip is not so common...

Brave words, Woody

Ossy, it could be any or all of a ridge dip, slope dishing, lateral spread at eaves, each of which can have different causes; he's not been specific as to where the bow is .

Plates and ties for lateral spread are fine as a principle, the number and position, together with plate sizes just has to be thought about, rather than blithely wanging them in at 2m centres and using a 9" plate. Half of the reason on older properties with ties that have depressions around the plates is not that the wall continued moving out, but the ties were installed and heated, the idea being that they would shrink as they cooled, thus pulling the walls together; if they got a bit overzealous on that front, the ties actually pulled the walls inwards around the plates.

As Woody says, it needs a survey at this stage, to determine what's what.

 

[dmills27]

Hi,
Thanks you all for your replies. The house is of 1930's style, and from looking no other houses in the street have the same problem. If we do go ahead with the purchase I would be getting a full survey which as you say would bring the problem up (if it is one) but before I spent £900 on the survey I just wanted to see if this could be a problem that would stop me buying the house all together e.g. if it would cost more the 5K then I would have to pull out of the house.

My concerns are if work is required then would where would the roof have to be accessed from? As the loft id converted it wouldn’t be easy to access from the inside (without ripping the ceilings, and walls off)

Thanks again!

 

[dmills27]

Also,
Not sure if it helps too much but I have attached an image of the house. Other point that I thought is that the addition of the velux windows could have been too much for the structure to take.

Untitled

• dmills27
• 15 Apr 2008
• 2

 

[^woody^]

.... before I spent £900 on the survey

Be clear what you will be getting for this survey.

If its a full Building Survey, specifically ask if the surveyor will be commenting on structural matters, as many will not commit themselves and will worm out with a comment like "The roof should be checked by a structural engineer" - this will then add another cost.

It may be more cost effective (and it pains me to say it) to get a structural engineer to comment on any significant structural issues which will include the roof and main structure, but will not include things like the general property condition and issues with damp, timber, plaster, windows etc

 

[Shytalkz]

It may be more cost effective (and it pains me to say it) to get a structural engineer to comment on any significant structural issues which will include the roof and main structure, but will not include things like the general property condition and issues with damp, timber, plaster, windows etc

You know it makes sense Woodster: you stick to your leaky CH pipes and leave the big stuff to the grown-ups

 

[Shytalkz]

Also,
Not sure if it helps too much but I have attached an image of the house. Other point that I thought is that the addition of the velux windows could have been too much for the structure to take.

Can't really see from the pic as to where the potential problem is, but presumably you mean that the roof has swamped, most markedly by the velux positions?

If so, the possibility is that the rafters to the side of the velux were not - at least - doubled up, to take account of the extra load onto them from the trimming rafters above and below. Complete failure is unlikely, although you might get some cracking of the internal finishes as a result of the deflection.

It can be strengthened, if necessary, from inside, but means taking down boarding, messing around with insulation etc. It might only need strengthening at those specific points, not wholesale, but without an actual look-see, it's impossible to say what would be required with any certainty.

You do need an SE to look at this aspect for you and to advise as to repairs required. In any event, if you've noticed it, a surveyor doing a HB report (or even just a valuation) should as well and make a recommendation for an SE to have a look.

 

[Shytalkz]

...as many will not commit themselves ...

Just about all, in my experience (and rightly so!).

 

[^woody^]

Call me a bit of a traditionalist, but there is nothing (except services) in a domestic property that cant be surveyed and assessed by a 'proper' building surveyor.

 

[JohnD]

I suppose the extent of a normal survey will depend on how fast the surveyor was going when he drove past the house and looked out of his car window.

Is there evidence that the loft conversion was done in accordance with building regulations, that plans were submitted and that it was inspected? there are lots of shady and amateurish building jobs done on the sly.

Also see if the vendor will let you into the loft to photograph it, and if there is any way to view the standard of construction and any roof timbers that have not been plastered over (often there is a little "crawl space" cupboard at the edges going into the eaves)

Be aware that this year there are lots of houses for sale, at dropping prices, and there is no reason why you should buy one you have doubts about, when there are plenty of good ones to be had.

Even better if you can find one that was built as four bedrooms (if that's what you need) rather than a small one that has had bits nailed on. I have my doubts about loft conversions in most smallish houses as you lose quite a bit of space with a proper staircase, and it is never as good as an original build.

 

[Shytalkz]

Call me a bit of a traditionalist...

Deluded more like

 

[dmills27]

Thank you all for your replies! I think what I am going to do first is double check that all the correct paperwork has been obtained i.e. building reg sign-off, planning permission etc. Then if all that is OK I will see about getting a structural engineer to look at just the roof. I think I can get the house at a very good price , especially if I can go in with my eyes open and know exactly what needs doing; it will all help with the negotiation!