Temporary purlin support.

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I'm converting a roof space into a room, PP acquired. Building inspector on board.

In order to get the maximum head height I'm planning on dropping the floor as room below can afford to lose a few inches in ceiling height.

In the roof space there is a purlin (see picture) spanning 3m approx. Supported in wall at both ends. A couple of feet from one end is a lap joint, with a post below it going down to a beam spanning the ceiling. Again this is supported at both ends and the current joists are nailed to it.
Purlin is about midway between brick supporting walls the rafters rest on, walls about 2.6m apart.

I was hoping to remove/replace the floor without opening up the roof just yet, kitchen below and we are living here during the work.

Would bolting a couple of lengths of timber either side of the purlin, spanning the lap joint, provide enough support to remove the post and floor joists, without the roof collapsing?
Any other suggestions as to how to safely prop it until the new floor is in.

IMG_20210507_154527696.jpg IMG_20210510_142510533.jpg IMG_20210510_142419545.jpg
 
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The purlin supports the roof, your SE can calculate what is needed, possibly a steel beam. As for the joists in the loft, I believe they tie the walls and stop spread, so removing them could cause big problems, no matter how strong the purlins.

So your plan could leave you with a dropped floor and an opened up roof but not as you intend.

Suggest you take on an SE every step of the way.

Blup
 
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I understand that, and have had SE involved. Due to a total lack of interest and or too busy, I have not been able to find a builder and so am doing the work myself.

I'm asking for the best way to support the purlin whilst the floor/ceiling is removed, so I don't have the roof potentially collapse, before it (and the purlin) is removed later on from the safety of a nice new strong floor.

For fullness (is that a word) this is what's happening. A, B and C are 9" brick walls. The ceiling between A & B is being dropped to give more headroom, the existing 2nd floor rooms floors are about a foot lower. The current floor/ceiling is just a load of 3x2 joists resting on what appears to be a 2x1 nailed to the wall.
Once the new floor is in the front section of roof will be removed and a large timber framed (gable) dormer extension will be constructed.

crosssection.jpg

The purlin is approx. halfway between A & B, a distance of just over 2.6m and spans about 3m. It is approx. 140x70mm section timber. Tables suggest it's undersized, but the house was not constructed when modern tables were written.

So could I bolt either side spanning the join to support it, or would it be safer to punch a couple of holes in the ceiling and prop it up from the floor below. 2nd option obviously makes fitting new floor more awkward.
There may well be 3rd or 4th options I've not thought of...
 
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The pile of joists have structural significance, they are more than just a ceiling support. The 2x1 (I suspect it may be more) is probably the wall plate. Can you post a pic?

Blup
 
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3x2 joists notched over and skew nailed into the 2x1 which is nailed to the wall. Other end are skew nailed on to the front wall plate.

floor1.jpg
 
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Maybe the SE could design the new floor and that could be put in before removing the old one, thus maintaining support for the walls (or even enhancing it), possibly for the purlin as well.

Blup
 
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I couldn't figure it out at first, but it's more like a first floor extension with vaulted ceiling dormers? I guess you want to remove the lower beam, can't you get the new joists under it?, you don't have to drop the new joists into the hangers from above so if they are going below the existing.... Are you planning to temporarily support the purlin off your new floor joists? might be ok or you might want a couple of acrows underneath to be on the safe side - if you use two with a timber between you can probably place then in a better position in your kitchen compared to a single one in the middle. As the roof is coming off anyway your only real concern is that the rafters could settle a bit and push loose the top few courses of brickwork on the outer wall.

Make sure any window lintels on the external wall a suitable for carrying the new floor.
 
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Yes extension rather than just a dormer. It will sit on the outer wall.
Building inspector has agreed that a pair of sistered joists sat on front wall replacing the current wallplate can used to hang the joist from, but that will entail removal of the rafters back to the purlin at least.
Probably a daft question but how do you fit joists to hanger without dropping them in from above?
Thanks for your help.
 
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Slide them up from below.

That was just too obvious I guess :oops:

Don't think I will be able to that anyway. I've more measuring to do (there will be 2 or 3 steps up to the new floor level even lowered) but I'm pretty sure the new joists will not go under the current ceiling.
Cheers
 

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