It is currently 28 Mar 2024, 20:44

Cathedral roof design for summerhouse

This forum is for any general questions, queries or plain old chinwaggery on Woody stuff in general.

Cathedral roof design for summerhouse

Postby oddsocks » 19 Feb 2016, 00:03

My wife has decided we need a small summer house in the corner of our garden. I suspect I won't (a) have the time or (b) be allowed to make it, so 'we' have been looking at websites.

EDIT 18/3/16...oops the power of google search - my wife just found this post when she searched for catherdral roof summerhouse :oops:

http://www.lancashiresummerhouses.co.uk/corner-summerhouse has caught my attention, partly because the page and products look quality, but also because they 'major' on cathedral roofs. They are Lancashire based but apparently have delivered and fitted to most of UK. Looking at the toggling image of the Seagreen painted one half way down the link, I started wondering where the 'centre' post of the roof is in relation to the two long right angled walls, the two shorter right angled walls and the diagonal door...is there a convention? Does the roof 'fan out' evenly to all points? I've spent a few evenings googling and looked in my reference books but cannot find anything that explains how to layout and construct such a roof....Can anyone help???

I will almost certainly go the purchase route given other committments, but curiosity drives the need to work how I would design it (ideally in Sketchup) and then cost and build it.

Thanks

Dave
Last edited by oddsocks on 18 Mar 2016, 13:57, edited 1 time in total.
User avatar
oddsocks
New Shoots
 
Posts: 115
Joined: 04 May 2015, 13:29
Location: Haverhill Suffolk
Name: Dave

Re: Cathedral roof design for summerhouse

Postby StevieB » 19 Feb 2016, 09:54

Looks to me as if the post is central, and the roof is constructed of 5 triangular sections, with the back 2 to the long walls being wider than the front 3. The roof sections are presumably then chamfered to allow a tighter fit from the inside where the triangles butt up against each other.

Give them a ring and they probably have constructional diagrams they can send you.

Steve
StevieB
Nordic Pine
 
Posts: 886
Joined: 21 Jul 2014, 21:47
Location: Chatteris, Cambridgeshire
Name:

Re: Cathedral roof design for summerhouse

Postby RogerS » 19 Feb 2016, 10:50

Hi Dave

Here's a different design that you might find appealing.

Image
If opportunity doesn't knock, build a door.
User avatar
RogerS
Petrified Pine
 
Posts: 13291
Joined: 21 Jul 2014, 21:07
Location: Nearly finished. OK OK...call me Pinocchio.
Name:

Re: Cathedral roof design for summerhouse

Postby Dave R » 19 Feb 2016, 12:25

Dave, it looks to me as if that "Corner Summer House" is 1/4 of an octagon. In SketchUp, draw an octagon with the Polygon tool and center it on the origin. Then draw lines from the origin out to mid-points at 90° to each other. The post to the roof will go at the origin.
Dave R
Nordic Pine
 
Posts: 653
Joined: 22 Jul 2014, 13:38
Name:

Re: Cathedral roof design for summerhouse

Postby oddsocks » 19 Feb 2016, 14:48

Thanks all - I've just realised I wasn't automatically subscribed to a post I created, so didn't have any emails.
(I've now found the setting in my profile to default to subscribed).

Once we have finalised the dimensions of the long sides (I think it will be about 2m) I'll give them a call for pricing and ask about the roof design.

Steve - that makes sense doing it in sections. I'll try DaveR's techique in sketchup and see where I end up.

I also need to read up on planning permissions as this will be on our back fence boundary (so I've read about 2.5.3 and 4m max heights before PP is needed, so need to understand where those measurments are taken (e.g. eave or apex?).

Dave
User avatar
oddsocks
New Shoots
 
Posts: 115
Joined: 04 May 2015, 13:29
Location: Haverhill Suffolk
Name: Dave

Re: Cathedral roof design for summerhouse

Postby Dave R » 19 Feb 2016, 14:58

Dave, while you're checking, look at fire related regulations. Very likely you'd have to put some fire resistant material on the outside of the back shed walls.

As you are drawing it in SketchUp, make components of the parts and copy them as needed. Since many parts will be similar, you can copy the components. Working with your model centered on the origin will give you a good reference for rotating copies.
Dave R
Nordic Pine
 
Posts: 653
Joined: 22 Jul 2014, 13:38
Name:

Re: Cathedral roof design for summerhouse

Postby oddsocks » 19 Feb 2016, 20:44

Thanks Dave- I will check re fire requirements, but I have never seen it mentioned before for a garden structure. The summer house is only for summer use (as the name implies!), not for working in, so it won't have power or lighting, just be a relaxing place to look at the garden.

re sketchup, i've never centred my designs on the origin but that makes sense when rotating components.

Dave
User avatar
oddsocks
New Shoots
 
Posts: 115
Joined: 04 May 2015, 13:29
Location: Haverhill Suffolk
Name: Dave

Re: Cathedral roof design for summerhouse

Postby Dave R » 19 Feb 2016, 20:49

oddsocks wrote:Thanks Dave- I will check re fire requirements, but I have never seen it mentioned before for a garden structure. The summer house is only for summer use (as the name implies!), not for working in, so it won't have power or lighting, just be a relaxing place to look at the garden.


It may not apply there but it's worth checking it out before you stuff that shed back into the corner if there's a fence as in the picture on the website. It'll be hard to add it later.

oddsocks wrote:re sketchup, i've never centred my designs on the origin but that makes sense when rotating components.

Dave


Generally the only time I center the model on the origin is when it is something has radial symmetry but in this case, centering the back corner post on the origin will make modeling easier.

Best. and have a great weekend.
Dave R
Nordic Pine
 
Posts: 653
Joined: 22 Jul 2014, 13:38
Name:

Re: Cathedral roof design for summerhouse

Postby oddsocks » 17 Mar 2016, 23:18

Thanks Dave R for the centering technique - I've now mastered that and watched these tutorials from Matt Jackson which gave some good insight...There are two, the second longer one shows the detail used to construct the model.
http://www.finehomebuilding.com/item/26 ... h-sketchup

I've been doing a lot of searching for pentagonal corner sheds/summerhouses etc and finally 'stuck gold' when downloading the models above from the 3d warehouse. ([i]I edited this 18/3 as I found the link)[/i] A search for 'shed hipped' revealed this model for an 8' corner summerhouse with hipped roof
https://3dwarehouse.sketchup.com/model. ... 9792152961

This model looks to be the one used in this sequence of photos (the website link is credited in the 3d workshop model).
http://www.jakeandkaren.com/housesite/shed.html

Using the sketchup dimensions, the walls are 6' 3" tall (its an american model in inches), the long sides are 8', the short sides 4' and the door angle 5' 7". The height of the roof to highest centrepoint is 8' 6" (roof heigh above the walls is 2' 3").

Looking at all the images and designs I've found, the roof in them has been built along the lines shown in the jakeandkaren sequence, yet the lancashire summerhouses cornerhouse image has a much bigger and longer centre octagon and set of smaller rafters reaching up from the bottom of that to (I think) the hip rafters. Presumably this makes for a stronger roof and helps stop any splay of the walls (???). Photos of JakeandKaren and other designs seem to imply it's not needed in an 8' building?

I'm still reading into this subject but getting more knowledge (or at least insight) every day. I now need to find links to help with the calculations for various slopes of roofs.

I did check - The Lancashire cornersummer house would cost over £5k even if I took some of the extras off, as the the delivery and erection cost to me added approx £1700 (it would incur 3 days with two overhights+ food /accomodation costs for the erection team), so I expect I'll be building my own... :)
Last edited by oddsocks on 18 Mar 2016, 18:09, edited 2 times in total.
User avatar
oddsocks
New Shoots
 
Posts: 115
Joined: 04 May 2015, 13:29
Location: Haverhill Suffolk
Name: Dave

Re: Cathedral roof design for summerhouse

Postby Mike G » 18 Mar 2016, 09:06

Just a note of caution about that set of photos, Dave. That roof only works because it is small and light. If that were larger, and tiled, it would be forcing the walls apart, which would mean that the plate on which is sits would need to be strong enough to resist the outward pressure, and be tied with strapping at the corners. Otherwise there would need to be something structural internally to resist the spreading forces.
User avatar
Mike G
Sequoia
 
Posts: 9834
Joined: 30 Jul 2014, 22:36
Location: Suffolk
Name:

Re: Cathedral roof design for summerhouse

Postby oddsocks » 18 Mar 2016, 10:02

Mike G wrote:Just a note of caution about that set of photos, Dave. That roof only works because it is small and light. If that were larger, and tiled, it would be forcing the walls apart, which would mean that the plate on which is sits would need to be strong enough to resist the outward pressure, and be tied with strapping at the corners. Otherwise there would need to be something structural internally to resist the spreading forces.

Thanks Mike, that's what I was wondering and trying to research options. My summerhouse will be the same size as that one (8') and also have a felted/shingle look roof. From more reading after I posted last night, it seems that either ceiling joists (to hold the walls in) or further stiffening of the hip rafters are used to avoid wall splay. We don't want ceiling joists so was looking into the stiffening of the rafters. I'll also use thick timbers for the wall frame and roof plate.

Another doc found (again american) describes the stiffeners as 'collar tie & beams' page 4
http://www.constructionknowledge.net/pu ... M5-426.pdf

I think another relevant example of stiffeners in my type of roof to keep the walls in is in this example (using the calculator with 'half centre' and 'extra creepers' selected). I set it to 5 sided (no corner pentagon option but I can do that in sketchup), radius 1600mm (approx 8' corner) and pitch 22.62degrees (5:12 rise)
http://www.blocklayer.com/gazebo.aspx.

my folder of bookmarks for this is growing :)
User avatar
oddsocks
New Shoots
 
Posts: 115
Joined: 04 May 2015, 13:29
Location: Haverhill Suffolk
Name: Dave

Re: Cathedral roof design for summerhouse

Postby Mike G » 18 Mar 2016, 10:45

It's not the rafters that are important in preventing spread, so you won't gain anything by bumping up the size of the hip rafters. In this circumstance, it is the tying of the wall plate into a continuous band by making sure the corners can't come apart which is important. If you visit the dome of St Paul's Cathedral in London you might get shown the steel wire that Wren built into the stone ring below the dome. It is pulled tight in a circle around the entire base of the dome to resist any spreading forces. You need to achieve a similar effect on a much reduced scale. Frankly, even a decent half-lapped joint at the corner junctions of the plates will probably do.
User avatar
Mike G
Sequoia
 
Posts: 9834
Joined: 30 Jul 2014, 22:36
Location: Suffolk
Name:

Re: Cathedral roof design for summerhouse

Postby oddsocks » 18 Mar 2016, 13:54

Thanks Mike, I was intending to make the wall plate with half lap joints and use two layers of timber with the laps on each 'reversed' so that would be strong enough. Hopefully by the end of the month I'll have a sketchup to share.

From the blocklayer calculator diagram, what would drive the design decision to add the 'half centre' or 'extra creepers' -is it to improve support for sheet material on the roof rather than roof frame strength?

Dave
User avatar
oddsocks
New Shoots
 
Posts: 115
Joined: 04 May 2015, 13:29
Location: Haverhill Suffolk
Name: Dave

Re: Cathedral roof design for summerhouse

Postby oddsocks » 20 Mar 2016, 22:41

oddsocks wrote:....... the lancashire summerhouses cornerhouse image has a much bigger and longer centre octagon and set of smaller rafters reaching up from the bottom of that to (I think) the hip rafters. Presumably this makes for a stronger roof and helps stop any splay of the walls (???). Photos of JakeandKaren and other designs seem to imply it's not needed in an 8' building?.....


I've done some more reading and now think that the extra timbers from lower down the kingpost to the rafters are acting as part of a 'Queen post truss' design and are in compression, stopping the main rafters from deflecting either due to their length or the load on them (tiles, snow etc.). They don't help with any roof splaying (as Mike said, this needs a roof plate able to resist those forces). In my mind (but not proven from reading), the introduction of 'half centre' timbers would also help avoid any roof splaying as they would lock that part of the roof to the design diameter. I think given a 2.4m x 2..4m roof this may be academic in real life with a felted roof, but part of being able to build it yourself is to over engineer :-)
User avatar
oddsocks
New Shoots
 
Posts: 115
Joined: 04 May 2015, 13:29
Location: Haverhill Suffolk
Name: Dave


Return to General Woodworking

Who is online

Users browsing this forum: No registered users and 13 guests