Roof rafters an inch lower at one end - Advice please?

[hammerswinger]

Hi,
No I haven't done the string line yet as it pouring with rain, I assume the string line has to be set level?

From my measurements the rafters are 20mm out over 6 meters then 6-7mm out over the other 3 meters.
The blockwork, wall plate and ridge board are all level give or take a couple of mm's. (4-5mm measured with a water level)

The wall seems to be parrallel to the existing but even if it was out I can't understand why this would cause the pitch of the rafters to be different, would the birdsmouth just not be further out (or in) along the rafter?
Could someone explain this to me as I don't understand?

As I've mentioned the lower end is going to cause the roof tiles to fall below pitch, by how much I'm not sure but as the tiles are only going to be at 17 degrees anyway I can't afford to loose pitch with them.


Cheers.

 

[joe-90]

I'd rather have securely fixed rafters an inch out than wedged and bodged rafters.

Have you checked everything with a laser level? Air pressure and surface tension can make a hosepipe very inaccurate.

 

[hammerswinger]

I'd rather have securely fixed rafters an inch out than wedged and bodged rafters.

Have you checked everything with a laser level? Air pressure and surface tension can make a hosepipe very inaccurate.

Yes I see where you're coming from but the tiles at the low end will be to low.

I haven't got a laser level, the water level is more accurate than the laser level anyway.


Cheers.

 

[hammerswinger]

The walls are not parallel, so the rafter level differs

Can I ask you to explain this to me please as I don't understand ?

The way I understand it, if the walls were not parallel altering the depth of the birdsmouth cut would keep the rafter at the same level, wouldn't it ?


Cheers.

 

[freddiemercurystwin]

The way I understand it, if the walls were not parallel altering the depth of the birdsmouth cut would keep the rafter at the same level, wouldn't it ?

If its done correctly. What length are the rafters? I'm intrigued as to why you think 1" will have a significant impact on the pitch let alone the kind of impact that would make the tiles watertight at one end and leak at the other.

 

[hammerswinger]

If its done correctly. What length are the rafters? I'm intrigued as to why you think 1" will have a significant impact on the pitch let alone the kind of impact that would make the tiles watertight at one end and leak at the other.

So even if the walls were not parallel the rafters could be kept level by adjusting the depth of the birdsmouth cuts, thought so.

The rafter length is 2860mm

The 1" lower rafters are causing the fascia board to lift the front edge of the tile by the same amount, I haven't measured it on the tile but on paper I think it will be about 4 degrees so that would give my tiles a pitch of approx 13 degrees instead of 17.

I'm not saying it's going to leak but it's not exactly ideal is it, I think it's better to sort out the problem now before all of the fascia tiles etc are fitted, as its quite a job then to put it right.

Cheers.

 

[freddiemercurystwin]

I haven't measured it on the tile but on paper I think it will be about 4 degrees so that would give my tiles a pitch of approx 13 degrees instead of 17.

Err your a bit off there. You will have a pitch at one end of 17° and where the rafter ends are 1" lower at the other end the pitch will be 17.47772102°.


edit Oh I see you mean the first tile that drains into the gutter? Don't think you really need worry there tbh.

 

[hammerswinger]

Err your a bit off there. You will have a pitch at one end of 17° and where the rafter ends are 1" lower at the other end the pitch will be 17.47772102°.


edit Oh I see you mean the first tile that drains into the gutter? Don't think you really need worry there tbh.

No...How can the pitch get greater when the front of the tile is higher....it has to be less.

Yes it is the first tile (Eaves tile) but the rafters are going to be out all the way up the roof towards the ridge plate, fair enough the amount of which the rafter is out will get less the further up the rafter you go as the rafter is at the correct height on the ridge plate.

It's a crap job, the joiner obviously didn't know what he was doing & I'm probably lucky it's only 26mm out, it could be a lot more.

The irony is that I was going to do the roof myself but I let the joiner do it to save time, looks like I've wasted my money there doesn't it.

Cheers.

 

[joe-90]

Was he a foreigner?

 

[hammerswinger]

No, why do you ask that?

 

[joe-90]

They usually do a bodge job.

 

[hammerswinger]

No I didn't have to look that far afield to get a bodge job, the bloke was local.

Whats the best solution to sort this then?


Cheers.

 

[Nige F]

So if you cut the fascia to follow the rafters it would be - in effect tapered to one end by c. 25mm ? with the bottom true and level . And if you fitted gutter to this tapered fascia @ the same distance from the underside of the eaves tiles - you would have a gutter with a fall , and it would not measure the same from the bottom of the fascia to the bottom of the gutter all along : . If you can do this and get the downpipe @ the low end - then you have an answer - and because gutter quite often falls (sometimes too much) on a level fascia , the look of it would not be odd particularly if you use a white gutter on the white fascia . Might be the answer

 

[hammerswinger]

So if you cut the fascia to follow the rafters it would be - in effect tapered to one end by c. 25mm ? with the bottom true and level .

Yes that is correct.

And if you fitted gutter to this tapered fascia @ the same distance from the underside of the eaves tiles - you would have a gutter with a fall , and it would not measure the same from the bottom of the fascia to the bottom of the gutter all along : . If you can do this and get the downpipe @ the low end - then you have an answer - and because gutter quite often falls (sometimes too much) on a level fascia , the look of it would not be odd particularly if you use a white gutter on the white fascia . Might be the answer

That's a very good idea & not something I had thought of, I'll have a think about it & if altering the rafters is going to be to much of a pain I may use your method.

I wouldn't hesitate to use your method if the roof was on a house, but as the extension is only a ground floor extension the gutter, fascia etc., is a lot more in your face than it is when up in the air on a house, what looks ok up high doesn't always look right when it's brought lower down if you see what I mean.

Thanks.

 

[hammerswinger]

All sorted now, the rafters are now all level with no fall on the roof

After a lot of measuring I had decided that the best solution was to re-seat the rafters at both ends of the roof (some down & some up) as this would cause the least disturbance, any other solution would have been a compromise and would of had a knock on effect. So the rafters on the LHS that were higher were reseated lower, with a couple on the RHS being replaced so they were higher, the removed rafters can be used on the other elevation of the roof that will drop down onto the garage roof as the rafter length on this side is shorter, so they're not going to waste.

The adjustments to the roof were done by the joiner who originally fitted the roof. I contacted him to explain the problem, he called in to take a look and agreed that 26mm was far too much of an error to reasonably work around, he had no hesitation in offering to rectify the problem, which was fair enough, as mistakes do happen. I explained my plan of lifting & lowering, he agreed that this was the best solution all round so we cracked on with it and had it done in a few hours.

I must admit I was very happy with the joiners willingness to resolve the problem, so any negative comments I made in my posts weren't warranted.

So all's well that ends well.

Thanks to everyone that offered advice.