Roof extention renovation

:?Hi,

Am I glad I found this site ! I have been reading with interest all you other renovators when it comes to roof extentions. I am part way through my extension (owner builder) and would appreciate some advice on my current situation to ensure I am not going to make some costly mistake down the track.

I have had my plans submitted to council and all has been approved but my plans that went to council have slightly different measurements on them. I have been looking up span tables feviorishly and found your web site !

I was part way through building my external deck (2.7m above ground) off the back of my house, and I am so impressed with the extra space I also want to convert it into part of the house (at a later time, trust me I will be posting more blogs when I sort out this one).

I have built the new deck with supporting 350x350 brick piers and 2x290 F7 treated pine bearers (max span 3.6m) (highlighted by cross in dwg, circles are post for upper room) to avoid cross bracing. Now this is where I am double checking to see if the existing bearer is able to support the new roof:

1) Therefore it becomes a lintel design? this is the first answer I need to know? I am looking up table in AS1684.2 2006 table 19 or 47 which suggests max span somewhere between 2.3m-3.9m (tbl 19) since my max RLW is 2.05, which is over the existing house so the moment around the lintel becomes smaller as you get closer to the lintel? how do I interpret the roof area supported at the concentrated load on the lintel given I have 4 posts supporting the hip of the roof?

I hope I am not getting top technical but a lot of things come to mind when you dont have any cheap or know of any good software to buy to keep my mind at peace.

This is my first post so I hope it works!

i have butchered a dwg submitted to the truss doods which makes it easier to understand the complexity here i have tried to colour code and use symbols to make it easier.

Rgds,

Barney

This roof extension will be marrying into a convential pitched roof. I was wondering what options I might have to do this. The truss manufacturer has designed a girder truss over the existing house where I assume I cut the rafters at the existing wall of the house and I fix to the girder truss to alloy removal of the wall (if I need to modify rooms). I would like to know best method of fixing here into hardwood (not sure of quality, red stuff extremely hard even my pasloe framer has trouble. I was thinking drill and screw using bugleheads?)

I was also considering cutting the rafter at the underpurling and butting the truss to the underpurling with maybe some modifications needed to the ceiling. I know that to do this I need to modify into the strutting beam.

It just appears logical to do this without sitting ontop of the old ones, given the ceiling joists are running in the same direction as potential truss members. I maybe creating some extra work here but I dont want to sacrifice any loss of strength, and in the back of the mind if I want to convert the area inside the convential roof area into a loft type room.

Could someone point me in the right direction to learn how to calculate/understand convential roof loads.

I am a bit concerned that where the strutting beam post supporting the underpurling is distributing is weight over 4 ceiling joists between walls, is a concentrated load? how do I know that when it was built how did they know how they did it without any Aust stds? I am trying to understand is it better to have a conventional roof vs truss roof vs steel roof vs exposed rafters.

Barney - I'm a bit confused about what you want to know.

In the extension shown on the roofing plan you need to cut the old roof back to the top of the hip rafter of the existing roof - unless you are trying for a box valley gutter where the new extension joins the house. Generally you cannot have exposed rafters in these old houses unless you substantially rebuild the roof.

A sub floor plan showing piers, bearers and load/bracing bearing walls will help in trying to answer your questions. You must also have an internal load bearing wall some where for your underpurlins - we need to know where these walls are and what is holding them up.

Hi Doogie,

Well you have ruled out one option that is a cathedral ceiling, thx.

The question I should be asking is, I am trying to build the roof first and then fill in underneath, walls etc, this is provided I can do so with the spans that I currently have, therefore all of my beams become lintels, correct? which will allow me to renovate under with shelter etc.

I went over the dwgs I have posted and learnt a bit more about the "triangle" for each post. The sub floor spans are as per dwg circles represent Piers 350x350 from L to R 3.58m,3.6m,3.54m. and the roof will be supported by 4 posts on top of the 2x290x45 F7 bearer, only the LHS bearer is directly over the pier.

Now I need to know if this is the case does the bearer become a lintel supporting a concentrated load? if so How do I calculate the roof area supported I have 4 options in the AS, 5,10,20,40 m2. The std tbl 19 only has RLW of 1500,3000,4500 etc if this is so can I linearise the measurements in the AS for max span allowable? If this is the case then I am in trouble for the 2 middle posts as I have calculated at max span of lintel 3.54m at 10m2 roof area supported. If they are classed as a distributed load (AS 1684.2 F7 tbl 17 upper storey with walls (but walls wont be there yet) then I am allright, hence build the framework of the walls and move on, except I havent got this on my plans with the council - do I need to put an ammendment in ?

Also the lintel on the LHS upper storey also becomes an issue, I currently have it on my plans as being supported through to the ground into a 450 fooring/pier but I really want to put a strip footing to allow for brickwork at a later date. I have fitted the 240x63 solid lam beam under the current top plate of the house on both sides and put a 35mmx70 F7 top plate ontop of it to match in (which can be removed if necessary fro 2 reasons) 1st maybe I am better of stripping some other grade of timber to get the right result for the lintel, or put another "packer underneath to get a 300mmm beam (what do I need to do to fit it??) 2nd is I might need to make this top plate smaller as to match ceiling heights as current roof has been birdmouthed.

I have a fairbit of reno work to do under the house one is to make into habitable rooms with single leaf brick and somehow I have to put some draining in and allow for weepholes etc as the house is 50yrs plus. I plan on bringing in some big toys to ripp up the crappy 50mm concrete underneath hence I will put a proper footing in and do the sewrage work at the same time. So its about spending in the right areas first and maybe I can do so with using some acroprops/ temp props where extra support maybe needed. My biggest issue is under the current bearer as I have to excavate and join the exisiting piers together (again council....)

I have included some photos for clarity. You will note I changed the design from posts extending to ground to posts ontop of bearers to allow brickwork/frames under bearers at a later date, but now I might have to work from the ground up. Just going through my photo files it looks like I need to update some. the last photo shows the lam beam which has since been cut back and the post is now over the bearer approx 400mm towards the house and a top plate as mentioned earlier.

A picture is worth a thousand words. I lived in Qld for a year and I brought home the look of the wonderful Qlder:D

That is a nice result.