Roof height seems to be raised 18" - why?

[sgking]

Hi

Not sure how old my house is. I suspect 300 years, but possibly more. In the attic the roof timbers appear to have extensions fitted to raise the roof by 18" or so. I was wondering why this might be. I have looked at lots of photos of other roof timbers in old houses and not seen anything that looks the same.

My first thought was that in trying to adapt from thatch to slate, they raised the roof to alter the pitch so that the extra weight was transferred more vertically, but on that rationale I'd have thought lots of houses would be the same.

Does anyone have any suggestions?

Thanks

 

[stuart45]

Have you got a few photos of the roof structure?

 

[sgking]

I have got some somewhere yes, I'll have a dig and see if I can find

 

[sgking]

Photos are on my PC so these are just photos of the screen, hence the poor quality. The original timbers obviously look alot older than the timbers used to adjust the roof height. Ignore the green treated wood and white roofing 'felt', that was an extension from 2010

I think I was being conservative saying 18", looks more like 2 foot or more.

 

[stuart45]

It looks like a Truss roof, which is when you have a few trusses which take the weight of the common rafters.
Thatch needs a steeper pitch than slate, so I doubt if the change from thatch to slate was a reason to alter the pitch. Also the steeper the pitch, the heavier the roof.

 

[Stevers]

Although crudely done, the big timbers look like structural members (probably acting as trusses) that always supported a roof structure that was above them.

Our house is 1879, but we have something not dissimilar, but in pine, with two heavy intermediate 'A' frame trusses with heavy purlins that carry the skinny rafters above that only need to span the purlins.

 

[stuart45]

Although crudely done, the big timbers look like structural members (probably acting as trusses) that always supported a roof structure that was above them.

Our house is 1879, but we have something not dissimilar, but in pine, with two heavy intermediate 'A' frame trusses with heavy purlins that carry the skinny rafters above that only need to span the purlins.

My daughter's got a terraced house built around the same time, and she's got a Truss at each end, but the purlins don't sit on top, but are fixed to the sides. The common rafters top is inline with the trusses.The squirrels have been chewing up one of them.

 

[Stevers]

Some very average photos taken on film from 1997. The purlins are notched into the A frame, but are mainly above. The fly in the ointment for me is the dropped ceilings at the rear of the house. I had fondly imagined that that nice strong leg visible below the ceiling carried on up the roof, but as can be seen here it doesn't, well not at full size anyway, so I'm wondering what is holding it all up. Best not to wonder I suppose!

For completeness the dropped ceiling was insulated with 80mm Celotex with 50mm deep battens to give a 50mm airgap - no problems with that so far.

 

[sgking]

Thanks for your replies!

So do you think that the roof has always been this way and it's just how it was constructed? The 'raised' parts look newer to me, , as do the rafters and purlins. Like they have been added at a later date

I need to get up there and have a good look for clues that might help with working it out

 

[Stevers]

So do you think that the roof has always been this way and it's just how it was constructed?

Only some of that roof is original - agreed. Whilst the rafters and purlins may not always have been the ones there now, I reckon the ridge pole would always have sat in the crook of the frame as it does now, with the slope of the roof being the same as the heavy frames. That would suggest to me that it hasn't been raised.

Old original thatch roofs are almost self supporting on a fairly light frame of poles. This is not the kind of structure you can hang slates on, so the more modern timbers could have been put in for the slate roof.

 

[stuart45]

There wouldn't be a need to increase the pitch. Thatch is normally at least 45°, and often more. A roof is designed to send the load down the walls to the foundations whatever the pitch. If it wasn't, the roof would spread and push the walls out.

 

[sgking]

Thanks for your replies, much appreciated. I want to go have a look around now. The spiders up there are seriously freaky mind, deep breath!...