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Doubling up rafters


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@Dee, i have to say that there should be 1:5 sectional detail drawings from the architect. this should all be drawn for you.

 

by headers, do you mean the timber across the width of the opening? if so i'd go with a double 6 x 2, joist spacing at 6 x 2 at 600mm  centres especially if the opening is 2.4m.

joist sizing as a rule of thumb, 6x2 =12+1 gives a span of 13', rafters 6x2=12-1 gives a span of 11', this works for all sectional sizes.

this doesn't work for trimmers/trimming joists

simon

Edited by Simplysimon
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A quick update photo on the weekends progress. 

I'm getting building control intomorrow for his opinion before we go any further....

If anyone spots anything wrong or missing then feel free to comment.... DSC_0619.thumb.JPG.ac284bac18851b50ba55b9f1a642b3c4.JPG

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Top front horizontal in the photo is 2x4 but another one to go on top..... So will be 4x4.

On the cheek rafters is a temporary brace.... is that what you mean? 

The front elevation is 2.2 with a 920 aluminium window and all that front sits on the steel you can see in the other photo. 

The corner posts are made of 2x4 and another at right angle 

Feel free to put me right! 

  On 12/03/2017 at 18:21, Simplysimon said:

 

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Top front horizontal to on the weekends progress. 

I'm getting building control intomorrow for his opinion before we go any further....

If anyone spots anything wrong DSC_0619.thumb.JPG.ac284bac18851b50ba55b9f1a642b3c4.JPG

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Upper end supported on brick wall with wall plate ontop (into attic)

Did a bird mouth notch.

See your point on rotating top timbers 90 degree,

Haven't glued anything until BC have been to look  

NB... We bought the house with planning already granted so we're going with what we have, there are no sectional drawings of any great detail 

Edited by Dee
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sorry, i meant the, soon to be cut, upper ends of the rafters.

 

have never taught cut hip roof by long distance before, suppose there's a first time for most things, you're about two weeks too early as i'm doing a cut hip roof and could have recorded it, but here goes - 

do you have a roofing square or do you have any experience of technical drawing? you will really need one method, i suppose laying it out on the ground full size is an option.

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Yes they will be cut off but ran out of daylight. 

Roofing square, yes. 

Technical drawing  experience, no. 

This is the first project that is truly beyond me so it is husband who drives this one. 

 

Edited by Dee
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No hypotenuse. 

Cut end of rafters? You tell me please  ?

This week I will be filling in the cheeks with vertical studs and the window elevation and making good the old roof (either side of the cheeks) with new felt and battons....  ready for working on the roof this weekend.... Please carry on advising when you have time, much appreciated 

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good stuff, dug out a dormer detail from 30yrs ago, first house!

dormer walls, 50x100 uprights @400crs with 50x100 top and bottom runnners, double uprights at window openings. 75x200 bridle joist at top cut ends of rafters, trimmers above windows were 2 x 50x200, if you were allowed 2 x 50x100, happy days.

 

simon

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@Simplysimon. We've done everything you did upto bridle joist?

Could you expand on that please ? 

BI suggested cutting existing rafters off at top,  vertically at bird mouth notch so they sit flush with front of wall plate, then some fixing for peace of mind. 

@ProDave. I'll post pictures tomorrow... Got too tired wrestling with huge tarps that have a mind of their own! 

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  On 13/03/2017 at 19:16, Dee said:

 

BI suggested cutting existing rafters off at top,  vertically at bird mouth notch so they sit flush with front of wall plate, then some fixing for peace of mind. 

 

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referring back to your pic yesterday at 13.38 the rafters have been cut and bridled, no birds mouth at top.

when you support the ceiling joists with acrow props and cut the rafters, the ends will need to be bridled to carry their weight and the loads imposed on them. these loads are then transmitted to the outer rafters you have doubled up and then to wallplate, walls and foundations. 

are you using 4x2 or 6x2 for new ceiling joists?

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Yes, using 6x2 for the ceiling joists  

 

There is a blue brick wall that separates a bedroom from the room that is being created by adding the dormer, The rafters that have been cut at head height,  rest on the purlin in the attic above.... I cut them at the bird mouth notch that sat on the wall plate. . . . . . . .  ( bedroom wall) Does that make sense or am I confusing everything? 

I'll post a picture tomorrow 

 

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I'll get to the front elevation this week but I'm unsure how t deal with the window surround.  I have an aluminium window 920mm wide, I know how to create the carcass opening but how do I 'dress' the opening when the window is in... I can't visualise it... I'll be using hardi board to clad the outside... 

Sorry for so many questions! 

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you'll need a lead tray under the window, upstands at each end and returned up inside of window needs to overhang outside finish.  i'm afraid you're confusing things, could do with some pics as rafters normally only cut with birds mouth at wallplate on ext wall, they normally just sit on purlin. haven't heard of hardie board. found it as cement fibre board for int use, is it the cladding? http://www.jameshardie.co.uk/hardielinea-cladding accessories on the page and i'm sure they would advise on fitting.

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I'll get to the front elevation this week but I'm unsure how to deal with the window surround.  I have an aluminium window 1000mm wide, I know how to create the carcass opening but how do I 'dress' the opening when the window is in... I can't visualise it... I'll be using hardi lines weather board  to clad the outside... 

Sorry for so many questions! 

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Today's progress, cheeks up, lintel in and the start of the front elevation.... Noggins to go in but I'm waiting for scraps. 

Tricky getting it square and plumb but managed it! 

DSC_0625.JPG

DSC_0626.JPG

DSC_0628.JPG

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