structural questions on roof topic

[marsaday]

i have been reading about someones poor attic conversion on the building thread, and this has prompted me to ask a few questions about my own. it will be happening next yr sometime.

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in the pic i hope to put a big long velux window in called the caribo (i think) window. it acts as a mini balconey.

the perlin in the middle of the roof will have to be cut. can someone tell me what i will need to do on this side of the roof.

Do i cut the perlin and lower it or simply remove it altogether?

how much will i need to uprate the existing rafters by?

what do the small vertical pieces of wood do ? they run from the roof into the ceiling joists. can these be simply removed?

are there any other potential problems people can spot.

there is a king beam in the middle of the roof.

 

[Shytalkz]

Well. you're obviously intending to make it into a habitable space so things that will need doing are:

• additional joists to cater for the increased occupancy load
  determine the method of support to these joists;
  determine the method of support to the rafters to facilitate removal of the purlin;
  probable strengthening of the rafters to cater for their increased span and loading from plasterboard and insulation;
  determine how the kingpost truss can be made redundant, allowing removal of the diagonals and vertical hanger.

The two sticks are hangers for the joists. Why they are where they are is anyone's guess: they could have been a later addition to cope with sagging and ceiling cracking; those joists might span further than others and the hangers provide an intermediate support; or a dwarf might have been living there secretly and put them in to string a hammock from.

 

[Deluks]

or a dwarf might have been living there secretly and put them in to string a hammock from.

Is this something you come across regularly as an engineer?

 

[Shytalkz]

Norfolk is full of the little beggars - think it has something to do with all the brother/mother/sister lovin' that goes on in the dark of night...

 

[Deluks]

Norfolk is full of the little beggars - think it has something to do with all the brother/mother/sister lovin' that goes on in the dark of night...

Stick that on the invoice... £150 - for calculating excess dwarf loadings.

You'd have cleaned up on this job

 

[Shytalkz]

Haha: excellent!

 

[noseall]

nice lookin roof.

especially that gable/chimney detail.

 

[marsaday]

here are some more. Do you think i will need a structural eng for calculations or will the architectural tech. be able to do everything?

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[noseall]

Do you think i will need a structural eng for calculations or will the architectural tech. be able to do everything?

there are everyday things that an architect could take a calculated guess at, knowing that the structure is going to be more than safe, if he over specifies a steel beam or a ceiling binder or purlin, for example.

but, there are some complex loading issues that only a structural engineer should be dealing with.

a lot of architects/designers work in tandem with a preferred s.e.

 

[Shytalkz]

An architect/technologist will be mindful of the fact that his PI insurance doesn't cover him for design of structural elements - or if they declare it, their premium goes up shedloads, on the quite understandable basis that they generally haven't got a clue.

There are those who will still do the design, but then get an SE to underwrite it for them. For which the fee from the SE will be at least that which he would have charged in the first place (depending on how crappy the design was in the first place), so the client can often spend more than if the respective professions had kept to their own sides of the fence.

Your roof needs a bit more than guesswork - unless you want to use the builder on the other thread and dispense with the professions in their entirety, of course!

 

[marsaday]

i will be doing the work myself with a joiner.

i have had some plans ordered and am still waiting for them -£400. so after this i need to get a SE in to go through the details.

i hope to leave the king beam and supports in place. the only structural change will be fitting this long velux. obviously there is the new floor to go down, but we have a wall at the half way point where this will sit on.

there will be an issue with 1/3 of the floor however as this doesnt have a wall to use. not sure what will happen here.

 

[Shytalkz]

If they're on CAD, email them to me and I'll give you a price for the design if you want. Whoever does your design will require first and gf plans as well, to determine where the loads will/can go: a loft plan on its own is insufficient.

How are you intending to work around the KP truss?? If you are intending messing around with the purlin, which will obviously be necessary, you will be changing the loading pattern to the truss - which means that it will then be required to conform to current design criteria, which it probably won't. Not to mention that the two diagonal struts and the vertical tie will be rather in the way within the room....

 

[marsaday]

i was hoping we could get a door under the diagonal strut. the designer thought he might. then this would all become a wall and i would show off the king beam as a feature.

so if we cut a purlin what implication does this have then. if it involves a lot of extra work/money then i will have to shelve that idea and go with a std velux.

do you think by doing this we would need to get rid of the king beam and insert steel purlins for the roof ?

the drawings are not in CAD, he is doing them all on paper. he is an old guy so this is the way he works.

 

[marsaday]

i'm wrong. just been up to have a look. we cannot get a door through the diagonals and so they will both have to be cut as we will need doors on both sides. if we cut them, can we use metal to tie the king beam and central main rafters together higher up so it is not in the way of the top of the door.

 

[Shytalkz]

I thought you were being a tad optimistic in your thoughts regarding a door in the KP truss!

It might be possible to alter the KP truss into a QP type arrangement to facilitate a door opening, using steel flitch plates on the ceiling member to cater for the increased stresses due both to additional loading and the loss of triangulation from the diagonals, plus relocation of the purlin and consequent change of loading to the rafter member of the truss. But then, to some extent, the loss of the current layout would reduce its attractiveness as a feature in the wall...

If you want me to take a look, email me and I'll give you my details and you can send the drawings by snail mail.