tie-ing in extension at roof level

[climber101]

Hi, calling the experts again please -

I have ‘hipped’ roof style extension. My questions relate refer to around the area marked “Interface between this rafter and existing wall” in the attached sketch please.

My existing exterior wall has harling on it approx 10-15mm thick over blockwork.

1) when attaching the rafter labelled “Interface between this rafter…” in the sketch I’m believing I have to chase out an area of the harling the depth of the rafter plus some distance above it to put in lead flashing. Does that sound right ? and if so any recommendations as to what machine to use as I’m thinking I’m removing a foot or so wide strip at an angle

2) In practice I’m thinking when coming to the roof I would be doing this chasing and putting this rafter in first along with the hips and then putting in the other jack rafters – sound about right?

3) Any thoughts on whether it would be useful to make this rafter any thicker than the others to assist attaching flashing/whatever at the interface to existing wall

Sorry if I don’t explain well but this whole area of roofing is one that I am least confident with ! Thanks again for any help given..


View media item 8720

 

[^woody^]

This rafter would be kept 50mm off the wall, so that the laths can be fixed without the nails splitting them if they are too near the ends. The laths then go up tight to the wall/render. You can also fix a 50mm noggin at mid span if you like to remove any sideways twisting

Mark a line above this to the required height of the flashing and then cut this with a 4" angle grinder. Then cut a slot in the actual wall to fix the flashing.

If the render is loose, and will not retain an edge, then you may have to fit a stop bead just above the flashing and make good the render above

Don't bother removing the render below the actual roof line - only remove it for the flashing upstand

And use the same rafter section as all the others

 

[climber101]

many thanks woody you are a star . I will study/digest your good words in detail (..and doubtless be back with more queries...)

For some reason i was thinking having this end rafter bolted into the wall would add some strength to the roof so I am thinking it really is the hips rafters that will be taking majority of the roof load. I think i will go back to looking at exactly how to support the hip rafters on wall plate because i am thinking that is a key area for holding up the whole roof so want that design to be the best

 

[noseall]

the rafters hold up the hips! all the hips and ridge do is keep everything in a straight line. sometimes the hips can carry some of the purlin load but not in your case.

all the forces are than transferred to the wall plate.

there is no need to bolt the rafter to the wall, allow it to flex with the rest of the roof.

just make sure you fit a temporary 'joist' across the plates, to prevent unwanted spread, at least until you fix the floor joists proper.

 

[noseall]

above post based on a joisted roof.

 

[climber101]

Many Thanks noseall - that makes sense, when you say temporary joist across the plates am I right in thinking I’m wanting to get the timber frame inner AND roof on before outer brick (as opposed to build the inner to wall plate level and outer brick to below eaves put roof on and finish brickwork)

but I’m glad you said “joisted roof” because that takes me back to one of my original concerns ! So if I can call on your patience yet again please because here goes..:-

The first attached line sketch “top rafters” shows the general idea of the ‘top’ roof rafters.

My extension has a slanted ceiling section and then it goes flat higher up. I am lacking detail of what rafters to put in to create this flat roof section within my plans which could have had more detail.

The next drawing shows my thoughts as to what “under” rafters I could put in and the last drawing shows a closeup of what rafters to put in. I’m thinking a short upper wall plate which takes the hips and two rafters and a longer bottom wall plate which takes a number of horizontal rafters which both brace? and give me something to screw the flat ceiling onto.

I’m after some guidance/ opinion please on my thoughts on my proposed ‘under rafter’ arrangement ? – (I’m thinking I need all of this to brace everything up but what do I know..)

(I can’t seem to see any pictures of rafter design in this type of slanted then flat ceiling design in a hip extension arrangement ? but I have taken my thoughts from lean to type arrangements, I’m wondering how common this type of extension ceiling arrangement I’m describing above is)

Untitled

• climber101
• 18 Feb 2009
• 1

Untitled

• climber101
• 18 Feb 2009
• 1

Untitled

• climber101
• 18 Feb 2009
• 1