Approved Document Part A

[theoldun]

Chirpy,
Read your post.
Bad day to-day. Should be okay to-morrow and will answer your post in detail
Regards oldun

 

[theoldun]

Chirpy.
Bad day again yesterday. Sorry.
Your double door frame will be at 2100. Your dormer window should be at 2100, Line the two through and shows back plate at 2100.You know in your own mind that the detail on back plate will not work, so lift plate up to existing house plate level, lift top ridge up , and marry existing roof into the short leg of new roof,. and you will then have a 2400 storey height.
Working on your figures,.
Rear commons. Run =3500 at 40, rise above plate = 2937 = slope (hypotenuse) = 4569. Raffter size required either 47x195 C16 at 400c or centre purlin 63x275 or 75x223 C16 mid span built into existing house wall and new stud wall and 47x100 C16 commons at 400c
Front Main Roof. Run 4600, rise above front plate 3860 = slope (hypotenuse ) = 6005.
Not sure whether we can explain this, but would suggest that providing Flitch has been designed to take joist load, snow load and tile load you fix Flitch in at 2400 from under side of Flitch to floor level to collect ceiling joists on by hangers and all front rafters to both main front roof and side roof
Front small roof. Run 3600 = rise above front plate 2853 = slope of 4438.
Back small roof. Run 2700 = rise above back plate 2266 = slope of 3525.
Conclusion. Flitch would be approx half span on small roof , third span on main roof and if same size purlin was fixed at two third span on main front roof same as back roof then you could have used 47x100 on all rafters,but you would need a purlin mid span on the small back roof. Suggest you go 47x125 over all to be on safe side.
Regards king post. A king post supports a beam below from a beam above and in our opinion it would be putting to much stress on ridge board, If you have mid span purlins, then you are covered.
Regards 47x100 studwork It would not be what we would use, but it will do the job with staggered double head plates We would use 47x125 as it makes it easier to comply with L1B U values, To achieve 0.28W/m2K in your walls 47x100, you will need 80mm Celotex GX4000 in studs and 37.5 PL4000 over stude with skim coat.
As we have no measurements and can not scale anything a lot of our thinking is guess work. Take your ceiling joists. We reckon they are about 6000 to 6500 long? We know what we would do, but what does your clever dick Arch of SE say about them?
Possibly we are missing a point as we have no first floor plan, but where will your studwork be for the flank and the main roof gable from the back wall of the small room with doors out to the front elevation. Both ridges and front purlin will have no support under them? Do you understand what we mean?
This is only our opinion Chirpy and it is up to you to check it out.
One other thing, hope you understand the difference between pitch line, Hypotenuse and HAP
Regards oldun

 

[chirpychippy]

Oldun, firstly and more importantly I am sorry to hear that you have been having some "bad days". hope you don't have to many more.



Thank you for all the details you have given me in your post, it is mind boggling how one person can know so much, so thank you once again. I rang the architect on the way home from work and asked for verification of the storey height pointing out that the drawings weren't much use and whether there were any working drawings, as you suggested. He didn't know what I meant by storey height, so had to explain, I offered to heights 2.4 which I scaled and 2.1 which made more sense, he replied with, it will be whatever the storey height in the house is! In the house it is 2.4, so I went onto to say that even with 5x2 rafters we are to close to the underside of the existing gable soffit. Oh Yeh, but its only a drawing was the response.

The contractor and I had already discussed on site bringing the rear of the larger salt box roof into line with the existing house which I offered to the Archi, he is not to happy with this approach, something to do with settlement and sag cos they are pantiles and may lift when the new roof settles?! Yet to be resolved.

I also asked about the flank wall and the lack of anything to fix the tiles to above the rear of the smaller salt box roof. He said he thought I would be build a sort of stud wall off of the joists that are running along side the rafter to the small salt box roof! "FFS"

Again I queried what joists I was expected to put in to take the span of some 6.5 meters, and to take the load of some sort of stud wall that would be supporting a purlin should we opt for a more sensible rafter size.

Mr Archi is coming to the site tomorrow for a meeting to go over all of this as the only responses I seemed to get were, ummm, well, I see, its only a drawing.

HAP = Height above plate after the birdsmouth has been cut, subsequently pushes the ridge board up higher.

Hypotenuse, I know what this is but I do use a ready reckoner called the Bible by someone I cant remember. but I can fathom rafter length by the square root method if I leave my book at home.

Pitch Line? I think I do, but I am not sure.

I think my book of Eurocode 5 span tables is coming by Royal Snail, not arrived yet, I may not understand it so yes I will take you up on your offer should I get stuck.

Thanks Oldun, will keep you posted, off for a meeting and a chat with the SE, will keep you posted.

 

[tony1851]

Your architect seems to keep saying "it's only a drawing".

Unless the drawing bears some relationship with the house and extension, seems to me that he may as well just have done some doodles.

 

[theoldun]

Your architect seems to keep saying "it's only a drawing".
Unless the drawing bears some relationship with the house and extension, seems to me that he may as well just have done some doodles.

Tony ,
You would never believe some of the drawings we have had to work to over the years.
Welcome to an old bricklayers world. If you can not level it with a passing cloud or sight it up with a near by tree, then f*ck it, do it your way.
Trust that meets with Mr BAS approval
Regards oldun

 

[theoldun]

Chirpy,
Quote. Pitch Line? I think I do, but I am not sure.
Okay, you under stand HAP and the fact that it lifts the ridge and top of rafter up from the true hypotenuse.
The hypotenuse is the measure from the top external edge of wall plate and to where the rafter will hit the ridge dependent on depth of rafters you are using.
Pitch line will equal hypotenuse. Most critical line on any roof. Crown and stack your rafters, so that all bows along the top will be the same. On your pattern rafter mark your pitch line, which will also be your hypotenuse line. Your pitch line is measure down from your top of rafter at 90 degrees and is two thirds the depth of rafter. Example 47x100 pitch line is 67mm down, 47x150 is 100mm down. On a 40 degree pitch the pitch line is now the hypotenuse and the internal angle of your 40 degree seat cut and your 50 degree heel cut. Got it?
There is no reason why you can not throw a stud wall up at the back to get 2400 storey, but your joists will have to be bolted to rear rafters to form raised tie or the stud wall brought further into the buiding
Yes there is a slim possibility that new roof will settle a bit, but to overcome this knock a course of brickwork of existing gable wall , lay 75mm fibre glass up wall and stick additional purlin in there
Any further help you need, ask.
Regards oldun

 

[chirpychippy]

Hello Theoldun and Tony1851 I finished the roof in question a couple of weeks ago but just have not had the opportunity to reply. Eventually we received the SE Calcs in writing making me much happier to commence as follows:

In the end I raised the rear section of main saltbox to match the line of the existing roof rafters as proposed, rafters were 6x2 C24 birds beaked over 2 no. 63x200 C24 timbers at the front. This beam supported the 5x2 ceiling joists which also were bolted to the rafters with M12 Bolts front and back. The rafters either side of the dormer were doubled up not tripled or quadrupled. 2 no. Binders at 63x175 were installed at 1.9mtr c/c to support ceiling joists. All Beams and Binders were supported by 4x4 posts in the timber frame work.

I think a big thank you is in order to Tony1851 but more so theoldun for your teachings, BTW I have the span table book which I haven't looked at yet, but intent to if the work rate ever slows down or when I am on holiday and have the time and I meant what I said, if you have a charity which I can make a donation to, then please let me know, otherwise I will make a donation to a charity that is close to my heart.

Cheers Chirpy

 

[tony1851]

I meant what I said, if you have a charity which I can make a donation to, then please let me know,

How about the 'Charity for Old Bricklayers on Hard Times' ?

 

[theoldun]

Chirpy
Does me old heart good to know that you had a successful completion
In my opinion lad, you have the balls and guts to tackle any cut roof.
Suggest you advertise in local paper, cut roofs a speciality Not many lads around who know the difference between a King, Queen, Jack and Common. Charge top money for your knowledge and ability.

Regards Wet Manchester Tony. Pay no attention to what he says, as we have it from a reliable source that his ambition is to be a ecking comedian at a working mans club,. and he practises daily on this forum.

All old bricklayers are wealthy film stars with generous pension pots.

Any time you require a lift up lad, come back.
Regards oldun

 

[tony1851]

Regards Wet Manchester Tony. Pay no attention to what he says, as we have it from a reliable source that his ambition is to be a ecking comedian at a working mans club,. and he practises daily on this forum.