new roof - slight pitch increase question

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I’m in the process of replacing the roof on my house and am at the stage where I have exposed the rafter tails to check their condition ahead of adding a new fascia timber. I haven’t fully stripped the roof tiles yet – am waiting for a few days of guaranteed dry weather.

The house was built in 1964 and in the mid 70’s a 2 story extension was added to the one side – this was done to match the existing house rather than be built subservient – to the untrained eye the extension is barely visible.

Unsurprisingly the rafter tails on the 1964 house (4x2 timber) are not in great shape but salvageable with some new 4x2 battens on the ends to support a new fascia timber. The 1970’s rafter ends (also 4x2) are in much better shape however they appear to be at a slightly different pitch to those on the original house. Looking at the roof close up from the scaffolding it’s clear the roof tiles are not level across the span of the roof, there’s a degree of sagging up and down which is most apparent when you lay a long straight edge across the roof – you can see an inch or more height difference in how the tiles are laid, particularly where the house and extension are joined. I’m assuming this is a consequence of some rafter sagging or just the poor way the 70’s extension was added – I won’t know for sure until the roof is fully stripped.

Once I roof is stripped I’ll know for sure what the apparent variation at the eves end of the rafters is all about and if any rafters are in need of sistering or other remedial action.

Given I’m already committed to new membrane, battens and tiles as well as all new roofline components I’m thinking I may as well add new rafters and ridge board to the job and do the reroof completely – it’s just extra timber and labour at the end of the day.

A completely new level set of rafters will just make laying the tiles (interlocking concrete Marley Mendips) just so much easier, plus I’ll know the new tiles are all sat on a new set of timbers.

The roof pitch is quite low at around 17 degrees and I’m wondering whether I can increase this slightly to 20 degrees at the same time as installing new rafters. Of course this will increase my ridge height by around 20cm. This slight pitch increase and resulting slight roof length increase will also help me optimise the head-lap on the tiles – reducing from 115mm to 110 mm.

Now I know increasing the ridge height is a big no no unless formal planning approval is sought. Now the scaffolding is up I really want to crack on rather than delay things.

The ground level of my neighbour’s house is 30cm lower than me - the road slopes down, but what’s interesting is our ridges are the same height. My neighbours, neighbour is 30cm lower again but this time their ridges are at a different height to reflect the falling ground level.

It occurs to me that my ridge should really be 30cm higher anyway to account for our ground height difference and it does seem odd that the original 1964 builder, that built my house and that of my neighbour and their neighbour, didn’t fully allow the ridge height to fall as the road falls.

If I increase my ridge height by 20cm, would anyone notice, and anyway I could arguably explain any new difference only reflects the difference in the ground level between us.

What do Forum members think?
 
Your neighbours steeper pitch roof is a precedent for yours, so you should get planning permission IMO. Be aware significant roof work requires compliance with current high insulation standards under building regs.
 
Hi, thank you for the comment - yes I've measured my neighbours pitch and it is 20 degrees. I'm puzzled why the original builder didn't go for a 20 degree pitch for me with a resulting higher ridge line. Yes I've already had the LABC Inspector round regarding the reroof and all they wanted to see was 250mm of loft insulation - not really interested in the outside roof work! - we've agreed an extra 100mm is needed to be seen internally (I already have 150mm) - the Inspector even advised that if I choose to then remove it afterwards that is my business! My plan is to make a platform suspended on 4x2 to accommodate the extra insulation so I can continue to use the attic for storage. I don't think anyone will notice the relatively small ridge height change and even if they did I'd challenge them to say it wasn't that height originally - the pitch will match the neighbour, the ridge height difference, if measured, will be less than the ground level height difference between us - to my mind I'm basically correcting an error made 60 years ago!
 

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