# minimum pitch for roof?



## dom68 (11 May 2018)

hi all i have some rosemary roof tiles id like to use for my workshop roof. however my workshop will be subject to usual max overall height of 2.5 metres so id like to keep the pitch of the roof to the absolute minimum to maximise the height of the eaves. 

can anybody help with what the minimum pitch should be? 

thanks dom.


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## Woody2Shoes (11 May 2018)

If they're simple plain clay tiles, then a minimum pitch of 35 degrees is pretty much the lowest sensible - as long as the site isn't particularly exposed. People sometimes go a little lower - and double up on felt and increase the head lap, but I wouldn't risk for a biscuit as they say. 

Also, the shallower you go, the more tiles (and more cost/weight) you use to cover the same floor area (45 deg being most "efficient" in that way).

Cheers, W2S


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## Lons (11 May 2018)

What woody said.

I've done it a couple of times on small porch areas after being advised to double up on the Tyvek underlay. You will need to increase the tile headlap but should be aware that there is a maximum recommended headlap depending on tile size, probably will be about 90mm from memory.

I don't think I would do it on anything under 30 deg if it were mine.

Bob


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## dom68 (11 May 2018)

ok thanks for prompt response guys! my shop will be around 3.3m in width so with a 35deg pitch what would the max eaves height i could attain?

dom.


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## MikeG. (11 May 2018)

Woody2Shoes":2j0su9pf said:


> ......Also, the shallower you go, the more tiles (and more cost/weight) you use to cover the same floor area (45 deg being most "efficient" in that way)..........



But please don't use 45 degrees. It looks awful. Two and a half degrees either side is OK, but not 45.


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## MikeG. (11 May 2018)

dom68":lvnk6krd said:


> hi all i have some rosemary roof tiles id like to use for my workshop roof. however my workshop will be subject to usual max overall height of 2.5 metres so id like to keep the pitch of the roof to the absolute minimum to maximise the height of the eaves.
> 
> can anybody help with what the minimum pitch should be?
> 
> thanks dom.



These are a machine made clay plain tile, with a minimum pitch of 35 degrees, as has been said. However, permitted development rights don't say a maximum height of 2.5 metres......it's 4 metres for the ridge, 2.5 for the eaves if not within 2 metres of the boundary. So, you've got the choice of building 2 metres away from your boundary or simply applying for planning permission if you want to build closer than that and have a 35 degree pitched roof. For some reason people do seem particularly reluctant to seek planning permission, and can end up with a building which doesn't particularly suit them as a result.


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## dom68 (11 May 2018)

i could apply for planning permission but it just means waiting. i could really do with getting started asap. 

the 1st image below shows where im planning on building the shop. as you can see the garden slopes away from the house. would it be possible for me to gain a little bit more height for the building by digging down and levelling the garden as shown in the 2nd image? 

https://ibb.co/gTBH6J

https://ibb.co/fr33fd

will the max height of the building be measured from point A in the 2nd image?

thanks dom.

appologies.. very quick rough drawings!


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## Woody2Shoes (11 May 2018)

MikeG.":1h1w0xdj said:


> Woody2Shoes":1h1w0xdj said:
> 
> 
> > ......Also, the shallower you go, the more tiles (and more cost/weight) you use to cover the same floor area (45 deg being most "efficient" in that way)..........
> ...



I agree! It's only pretty recently that we've used degrees, the old boys would have used ratios - a bit like rise vs. going on stairs - a ratio of 11 (span) to 10 (rise) gives a nice 42.something degree pitch.

Cheers, W2S

PS a word to the wise - if you're going to excavate your back garden:
a) Don't underestimate how much material you'll have to shift;
b) Make sure you know where all the drains/wires etc. (yours and everyone else's) plus abandoned bomb shelters/soakaways/septic tanks etc. etc. are;
c) Make double sure you're not undermining your house or your neighbour's.


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## dom68 (11 May 2018)

ok i just had a quick dig in the garden.. i dug four holes in approx the places where the corners of the building would be. ive found that around 4/5 inches below the surface there is already around 8/9 inches of crushed stone.. any ideas on why this could be? 

a neighbour has told me a past owner of the house used to park lots of cars in the garden so maybe this why? theres actually some old metal gateposts on the outside of my fence possibly indicating a driveway? 

also at the back of my house in the direction of the slope is another house.. approx 18/20m from the back wall of my conservatory so could it be something to do with drainage?

thanks dom.

ps. the extent of the slope over the intended 3.3m span of my shop is around 300mm.


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## MikeG. (11 May 2018)

dom68":3ffclcwj said:


> i could apply for planning permission but it just means waiting. i could really do with getting started asap.
> 
> the 1st image below shows where im planning on building the shop. as you can see the garden slopes away from the house. would it be possible for me to gain a little bit more height for the building by digging down and levelling the garden as shown in the 2nd image?
> 
> ...



No, the height is (or can be) measured from the lowest point, and it's the original (or "natural") ground level that counts, so digging isn't going to help you. This is going to boil down to waiting for planning permission or giving up on the idea of using plain tiles, assuming you want to build within 2m of your boundary.


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## MikeG. (11 May 2018)

Woody2Shoes":31kdt7kp said:


> MikeG.":31kdt7kp said:
> 
> 
> > Woody2Shoes":31kdt7kp said:
> ...



Exactly. Although they worked in inches rise per foot. 11 inches in a foot gives an angle pretty close to 42.5 degrees, and 13 inches per foot gives 47.3 degrees........hence my "2.5 degrees either side" advice.


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## dom68 (11 May 2018)

ok thanks mike. any ideas about the crushed stone?


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## MikeG. (11 May 2018)

No, not without photos and a lot more info. However, if you look at the second link in my signature, you might find a way of usefully exploiting them.


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## dom68 (11 May 2018)

ok mike il have a look.. thanks very much for your help. 

dom.


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## Woody2Shoes (11 May 2018)

MikeG.":28pc7z2m said:


> Exactly. Although they worked in inches rise per foot. 11 inches in a foot gives an angle pretty close to 42.5 degrees, and 13 inches per foot gives 47.3 degrees........hence my "2.5 degrees either side" advice.



I think that my Edwardian roof must have sagged somewhat!! It's definitely closer to 10:11 than 11:12. I think that North American builders still use ratios (probably based on feet and inches as you say). Cheers, W2S


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## MikeG. (11 May 2018)

They were quite happy to work to half inches or smaller, so 10.5" to the foot or 11.25" to the foot, whatever. Of course it's not impossible that someone went their own way and did 10:11, but what I've read on the subject suggests it more likely that it was generally inches (+ fractions) to the foot.


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