DIY two storey extension

[noseall]

6" x 3" sounds way to lean for a modern roof designed purlin.

8" or 9" x 3" is fairly typical.

setting the purlin at midspan may allow you to use 100mm x 50mm rafters, but it will depend upon span and pitch.

the purlin will need to be supported off either a masonry wall or by using steel to span the walls and 100mm x 100mm props off the steel. again, this will depend upon structural layout.

the roof is unlikely to spread provided the existing rafters are fixed correctly to the existing ceiling joists. you could always prop the ridge board for peace of mind.

are the existing purlins propped off masonry?

a cut roof may need some degree of s.e. design or a lot of conversation between you and b.c.

are you planning on building the roof yourself?

 

[Chickenski]

Thanks again Noseall.

Span of new roof is approximate 10m x 5.20m.
Purlins are supported by posts sitting on double joists. If 6x3 is too flimsy should I change it or just continue with 8/9x3 in new part?

Rafters seem to be in a very good condition considering the house dates back to 1920s . However, joists run in a very peculiar way. Front to back of the house, with only one side having perpendicular joists to support the rafters. That means that on the other side (lengthways) joists are supported/fixed to wall plate and not joined with rafters!

I will of course prop up ridge board when taking hip blades out. Hopefully it will be enough.

Yes, I am doing it myself; not physically though. BC seems to have a lot confidence in me for some reason. After putting up very complicated steel he said the roof should not be the problem. Hmmm...

 

[Chickenski]

Sorry, forgot to add pitch of the roof; it stands at 40 degrees

 

[pantsmachine]

Good on you for undertaking a 2 storey diy proj. Not to burst your bubble but be aware that BC cats from the council do not replace an architect, yes they have knowledge but they are also harried and on many projects. Just coz he says its ok does not mean it is. My persnal view on this for posterity is yeehah for using the cheap labour, its a long walk from poland but an architect should have been involved and they don't cost too much. Mines a grand for drawings for a average size job including call ups and site visits whenever you need him, money well spent. Right off my soapbox now, good luck with the rest of the build and i look forward to seeing the photos which i am surpriesed you have not been posting along with your questions.....

 

[Chickenski]

Thanks for your encouragement. I am dead excited abut this project and also very anxious. Yes, I had plans drawn by architect and am in constant touch with BI who is also a structural engineer. All is going fine; we are cutting the roof and will be covering the main part with Permo Forte this weekend to protect it from rain. There will be another hip roof joining the main one and this is what I am anxious about.
Would love to attach photos but don't know how. Am taking lots of pics so let me have instructions how to do it please.

Speak soon

 

[Chickenski]

This was for PANTSMACHINE but I made a mess of it!

 

[Chickenski]

Good morning all!

Roof level wall plate: does it have to be bedded onto mortar with DPC underneath timber? Do I need DPC there at all?

Early reply would be appreciated. Need to have it in place today so it is ready to received roof timbers on Monday.

Thanks

 

[noseall]

no dpc.

you can bed on mortar or lay dry.

use mortar if you feel the masonry is either out of level, a little bit up 'n' down or that the wall plate needs picking up a little.

don't forget to restrain the wall plate before attempting to pitch up the rafters or you will end up spreading the plates. once you eventually fit the joists, spread will be alleviated.

we normally drop a couple of timbers across the plates until such time as to fix the joists.

 

[Chickenski]

Thanks Noseall!

Of course we will restrain it before doing anything else! Shall I also nail it to blockwork?

So far extended old roof and now coming to hip area... Old hip blades are massive: 2.5 inch by 9inch. Do we really need them as big as this? How do I connect old/new purlin?

Thanks

 

[noseall]

the hip blade on some roof's can help support the purlin ends.

so yes, if that is what is specified, that's what you must use.

if the hip was not supporting, and only there as a rafter end support, then you only need enough depth of timber to accommodate the splayed rafter end cut plus another 50mm in depth.

the weight of the rafters bearing onto the hip board gets transferred to the wall plate.

it's the same with the ridge board. its purpose is to keep the rafters straight and needs only to accommodate the rafter end cut plus another inch or so.

 

[noseall]

you can connect timbers with a scarf joint.

or, you could set the new purlin slightly higher up the roof, just enough to miss the existing, then run it along side the existing then bolt them together.

 

[pantsmachine]

For posting photos i use imageshack. Its free to set up an account and is a good site to upload and store your photos.

1 set up an account
2 follow email registration link to the site
3 upload your photos to be displayed to the site
4 use the website mail address for forums which will be dispalyed beside you photos to display on this forum(basic cut and paste from imageshack to your post on this site)
5 sit back feeling well chuffed with yourself(i know i did).

FYI try and set your digi camera to 1mb per photo max, faster uploads and faster for people to view as well.Good luck!

 

[Chickenski]

Thanks to Noseall and Pantsmachine!

I have reached an impasse!!!!!!!!!!!!! My plans suggest truss roof. I am doing cut roof supported on walls which already have a lot of steel beams/columns. There is obviously additional load from cut roof. I therefore need to build a supporting wall to accommodate the weight of ceiling, purlin with struts etc.

Hence my question, or rather BI question:

What is the maximum load bearing onto: 203x203x46UC S275. Span 4.2m

I have to convince BI my new cut roof is well within this maximum.

Thanks to all who are able to help

 

[AtoZ]

there is a book available in the library that gives you most of the sizes and spans of timber and things. it would answer a lot of the questions you have asked.
rafter sizes can come down to 100x50 if supported by purlins. recently, although regs said this was possible, my own inspector said i had to use 150x50 because of the need for insulation depth but that will have changed again since the new reflective insulation.

if your floor joists run different to your rafters, could you double up the joists directly below the purlins to take the load.
purlins are not there to actually take load. they are there to spread load and prevent a 'dropped' rafter.

another thing, if you intend to use the loft then you are likley to have to use a big sectional steel to support the floor.
why not do this now? it would allow the use of smaller timbers for the floor and solve all of the other problems.
.
your cut roof sits on walls, walls take the weight. trusses sit on the walls and design of them would decide on whether you needed a seperating wall, same as a cut roof.
it sounds to me that your inspector is concerned about your loft floor/ceiling rather than your roof. if you havent given him the detail to work out if you need a wall then i would presume he would insist on the roof timbers being big enough to be self supporting. i know i would if i were dealing with someone like yourself (no experience).
think about a loft steel, its an easy solution.

this is a bit hard when you cant see

 

[Chickenski]

Thanks AtoZ.
I have already resolved the question of roof support. My existing steel is sufficient for supporting wall and so the roof is now coming along nicely!!! Literally as I write this.

Question about roof covering. I am taking off existing hand made clay tiles. Some of them are damaged and I am not sure whether not to recover completely. If so, what is the best choice? My structural engineer suggested interlocking concrete tiles. About 50kg/m2 so not too heavy. How do they compare to clay? I am aware clay looks much better!
If I decide to recover completely, how much can I expect to get for my old tiles?

I will be covering the whole roof with Klober Perma Forte. At the moment I have nothing underneath old tiles!

Am going off on skiing holiday Dec 22nd. Can I leave the roof with Perma Forte only for this one week? Is it safe???