Roofing question

General wood working tips, tricks and ideas. Anything that doesn't belong elsewhere can be discussed here.
promhandicam
Moderator
Posts: 3451
Joined: Wed Oct 17, 2007 8:50 am
Location: Surrey / Hampshire
Contact:

Roofing question

Postby promhandicam » Thu Feb 14, 2019 11:18 pm

Evening. I would really appreciate some advise on modifying my garage roof at home - see below.

garage 1.JPG

garage 5.JPG


The garage is single skin, and the roof has a span of 5.4m a pitch of 45 deg and is 5.7m wide. The rafters are 5x2 and the joists 6x2. At each end the rafters have been doubled up. When I moved in, I boarded the loft and added a staircase and to date it has been used as storage. My son would now like to get a few bits of gym equipment (treadmill, rower, bike but not weights) and so I want to open the space up a bit. At present there are 3no 4.2 hangers from the ridge down to a 6x2 binder running across the joists. The binder isn't keyed into the brickwork. It is the binder and hangers I'd like to remove. Hopefully the following show the current construction.

garage 2.JPG

garage 3.JPG

garage 4.JPG


What I am thinking of doing is shown in the sketch below (clicking on it should make it large enough to read)

garage roof.jpg


Basically I am thinking of adding a collar about 1/3 up from the joists at each end, and then installing a purlin each side on top of the collar. The purlin would then have hangers down to a sole plate. I'd also add some noggins between the joists and add a binder above the existing collars which the existing hangers can be attached to before cutting them off. I realise that ideally the purlins should be keyed into the brickwork, but because it is single skin I'm guessing this would be difficult. Is this overkill or should I live with what I have or get a structural engineer involved? Just to add, I'm not planning on making it habitable, but I may put some 70mm insulation between the rafters and then p/b or ply the ceiling and possibly insulate between the joists.

Any advise would be greatly appreciated.

Tomyjoiner
Subscriber
Posts: 450
Joined: Mon Jan 02, 2012 5:51 pm
Location: cumbria
Contact:

Re: Roofing question

Postby Tomyjoiner » Fri Feb 15, 2019 8:08 am

structural engineer will want steels to cover his ar*e.4x2 ties below ridge on every rafter, dwarf walls in 4x2 double header boarded in osb3 for load bearing.

promhandicam
Moderator
Posts: 3451
Joined: Wed Oct 17, 2007 8:50 am
Location: Surrey / Hampshire
Contact:

Re: Roofing question

Postby promhandicam » Fri Feb 15, 2019 12:15 pm

Tomyjoiner wrote:structural engineer will want steels to cover his ar*e.4x2 ties below ridge on every rafter, dwarf walls in 4x2 double header boarded in osb3 for load bearing.
. . .which is why I don't want to talk to a structural engineer :lol:

Meccarroll
Subscriber
Posts: 753
Joined: Wed Nov 27, 2013 6:37 am
Contact:

Re: Roofing question

Postby Meccarroll » Sat Feb 16, 2019 10:58 am

Just a quickie: have you considered using a truss to support the purlin (locate it on the central pier)? 5.7m is quite a span for any purlin to cope with in timber. A central truss would half that.

You could make the truss so it top edge sits on the same plane as the ceiling joist but bottom edge hangs below. This would allow you to make it substantial in depth (to allow support to the purlin) but also avoid upsetting the line of the intended floor above.

I would simply take the purlin through the wall either end and let it rest on the brick wall (easy enough to do) shaping the ends as normal.

The 6x2" ceiling joist are a little under size for the span, 10x2" would have been better! So to help carry the load you could put 10x2" binders running behind the hangers at floor level (just above the ceiling joist). Take them the full length of the roof and strap them to the floor joist and hangers to stiffen up the floor area. Again they would rest on the central truss.

To make a truss you could double up rafters and bolt them together with spiked connectors. If you want to go a stage further use 8mm thick plate steel between the truss timbers Drilled at say 350mm centres and bolt through the truss captivating the steel in the middle (Forming a flitch beam). If you don't want to use steel consider using 20mm ply between the truss timbers, glue and pin it to one section then glue and bolt through the next captivating the ply in the middle.

Just a few quick suggestions to think about. Hope you don't mind.

Mark

Meccarroll
Subscriber
Posts: 753
Joined: Wed Nov 27, 2013 6:37 am
Contact:

Re: Roofing question

Postby Meccarroll » Sat Feb 16, 2019 11:08 am

Just another quick one: From what you wrote it sounds like the original binder and and 3 No hangers are primarily supporting the ceiling joist (stopping them from sagging in the middle and not a major support for the rafters). Collectively all the roof members help in supporting the roof and load but I would think from your description and section sizes that your main area of concern would be the floor.

Mark

promhandicam
Moderator
Posts: 3451
Joined: Wed Oct 17, 2007 8:50 am
Location: Surrey / Hampshire
Contact:

Re: Roofing question

Postby promhandicam » Sat Feb 16, 2019 2:41 pm

Thanks for the suggestions. Will give it some more thought as I can't do anything at the moment anyway!

thatsnotafestool
Subscriber
Posts: 4898
Joined: Thu Sep 27, 2007 5:27 pm
Location: Oop North where it rains
Contact:

Re: Roofing question

Postby thatsnotafestool » Sat Feb 16, 2019 9:28 pm

Why not pop over to TWH2 as we do have an expert onboard ! No, not me, silly.
The advantage of a bad memory is that one enjoys several times the same good things for the first time.
Friedrich Nietzsche

Meccarroll
Subscriber
Posts: 753
Joined: Wed Nov 27, 2013 6:37 am
Contact:

Re: Roofing question

Postby Meccarroll » Sun Feb 17, 2019 8:52 am

thatsnotafestool wrote:Why not pop over to TWH2 as we do have an expert onboard ! No, not me, silly.


That's very nice of you Roger!

LoL

thatsnotafestool
Subscriber
Posts: 4898
Joined: Thu Sep 27, 2007 5:27 pm
Location: Oop North where it rains
Contact:

Re: Roofing question

Postby thatsnotafestool » Sun Feb 17, 2019 10:09 am

Meccarroll wrote:
thatsnotafestool wrote:Why not pop over to TWH2 as we do have an expert onboard ! No, not me, silly.


That's very nice of you Roger!

LoL



Sorry, Mark...I meant 'in addition to the ones we have here'.... :oops: LOL !
The advantage of a bad memory is that one enjoys several times the same good things for the first time.
Friedrich Nietzsche

Meccarroll
Subscriber
Posts: 753
Joined: Wed Nov 27, 2013 6:37 am
Contact:

Re: Roofing question

Postby Meccarroll » Sun Feb 17, 2019 11:25 am

The below link should help with recommended timber sizes and spacing for your roof (useful to consult). The floor is different but you can find recommended sizes online for your floor span if you want. We used to use a rule of thumb:

1. Span divided by two (convert this figure to inches) then add two inches. This gives the depth of joist for a floor with joist spacings at 400 centres and 2" thick joist.

So if the span is 10 feet we would divide it by two giving 5 then we would add two to the five 5+2 giving 7" depth of joist for a 10 feet span.

The link below is for roof member sizes, and is a link to Eden council.

https://www.eden.gov.uk/planning-and-building/building-control/building-control-guidance-notes/pitched-roof-timber-sizes/


Roger, I am sorry as I was only joking!....... I had the devil in me :twisted:

Meccarroll
Subscriber
Posts: 753
Joined: Wed Nov 27, 2013 6:37 am
Contact:

Re: Roofing question

Postby Meccarroll » Sun Feb 17, 2019 11:45 am

Same information as in the link I gave above.

Image

Image

Image

Image

promhandicam
Moderator
Posts: 3451
Joined: Wed Oct 17, 2007 8:50 am
Location: Surrey / Hampshire
Contact:

Re: Roofing question

Postby promhandicam » Sun Feb 17, 2019 10:45 pm

Thanks Mark. Very helpful.

Steve

Meccarroll
Subscriber
Posts: 753
Joined: Wed Nov 27, 2013 6:37 am
Contact:

Re: Roofing question

Postby Meccarroll » Wed Feb 20, 2019 6:44 pm

promhandicam wrote:Thanks Mark. Very helpful.

Steve


Glad to help. Hope that finger repairs V.soon ;)

thatsnotafestool
Subscriber
Posts: 4898
Joined: Thu Sep 27, 2007 5:27 pm
Location: Oop North where it rains
Contact:

Re: Roofing question

Postby thatsnotafestool » Thu Feb 21, 2019 5:52 pm

That's a cracking link, Mark. But I'm curious...are you up in Cumbria then ?
The advantage of a bad memory is that one enjoys several times the same good things for the first time.
Friedrich Nietzsche

Meccarroll
Subscriber
Posts: 753
Joined: Wed Nov 27, 2013 6:37 am
Contact:

Re: Roofing question

Postby Meccarroll » Sat Feb 23, 2019 2:36 pm

A bit more information on floor timber sizes which may or may not be useful:

Image

Image

Image

Image

Above taken from Lancaster City Council: Homeowner Guidedance In the Building Control Section.

The above are worked for domestic floor loads. Your roof has a pitch which means you can not use all the floor span. In effect your loading is very likely to be less than the above for several reasons, You are not likely to load all of the span with boarding etc (you also may not have plasterboard on the underside further reducing the load), meaning the above sizes may be oversized for your actual load conditions.

(Not near to Cumbria Roger, otherwise I'd be pestering you to see all that wonderful woodwork you are doing)

Mark

jfc
Administrator
Posts: 10657
Joined: Thu Sep 27, 2007 3:39 pm
Location: London
Contact:

Re: Roofing question

Postby jfc » Thu Feb 28, 2019 8:50 pm

Rather than your floor plate to hold the new purlin / wall you could double up some 6-8 x 2 Depending on the span and let the walls take the load . Or make a box beam up . If you do the box beam you could make it in the loft space .


Return to “Woodworking”

Who is online

Users browsing this forum: No registered users and 1 guest