Any downsides to removing purlins and using ridge beam?

[Digmixfill]

Hello all,

 

I've currently got 3.25"x2" rafters and purlins with a ridge to wall plate span of a little under 3m. I'm considering upping the rafters to 125x47mm and installing a ridge beam.

I can only see advantages with the change. Then I think - If that is the case why aren't all room in roof ridge beam and not purlin?

 

Are there disadvantages that I should consider?

[Mike]

Nothing that would stop me doing it! Provided your new timbers are correctly dimensioned and you insulate it to at least Building Regs standards, of course.

 

4 minutes ago, Digmixfill said:

why aren't all room in roof ridge beam and not purlin?

It costs more to build and a little more to heat, and there's a loss of storage space.

[Digmixfill]

3 minutes ago, Mike said:

Nothing that would stop me doing it! Provided your new timbers are correctly dimensioned and you insulate it to at least Building Regs standards, of course.

 

It costs more to build and a little more to heat, and there's a loss of storage space.

 

Building control will be checking everything, as usual. Like most on here I plan to over insulate

 

It's already designed to be a room in roof, so no storage space to lose.

[Iceverge]

Why stop at 125mm.

 

220mm with blown cellulose in between is where it's at. A/T membrane and 47mm counterbattened and insulated service cavity. 

 

 

 

[joe90]

For my warm loft (used as storage and MVHR kit) I used 300mm I beams with ridge board full fill with rockwall and lined with OSB3 bubble glued together.

Edited July 4, 2023 by joe90

[Digmixfill]

Our rafters terminate in the cavity behind corbelling. I would think there is a limit where lowering the ridge beam height to accommodate the deeper rafters would cause the end of the rafter to kick up tiles. All of our second floor is room in roof and head height is limited in what will be a shower room.

 

I can play with the space available to see what I can get in.

 

Still no downsides to the idea though

 

 

[joe90]

10 hours ago, Digmixfill said:

I would think there is a limit where lowering the ridge beam height to accommodate the deeper rafters would cause the end of the rafter to kick up tiles.

You are not altering the angle of your roof! So why would the lower ridge beam kick out the lower ends . An additional ridge beam could be added below whatever ridge board you currently have.

 

[Digmixfill]

To keep increasing the rafter height and lowering the ridge beam position, at some point I will need to start chopping into my new internal walls to lower the wall plate. I can carve the nose of the rafter to fit into the space behind the corbelling, between the external brickwork below and the tiles.

 

 

[Digmixfill]

Just quickly checked and I can fit 150mm rafters without any issue.  Because the outer shell is anything but straight the space between the current roof and the new inner leaf varies and in some places I could fit 200mm.

 

This reminds me to post another thread about how to deal with this...