L Shape Dormer Loft Conversion

[sylvane]

Hi everyone. 

 

I came across this site while researching ways to maximise the floor to ceiling height for a terrace loft conversion.

I was hoping to get started in the next few months (I've shortlisted a few builders) but am a bit worried about head height. 

 

The initial survey shows that I only have 2150 between the top of the existing 4X2 ceiling joist and the underside of the ridge beam. I'm therefore pretty concerned about the final floor to ceiling height once the new floor and flat roof is built. 

 

I don't have the option of lowering the 1st floor ceiling and raising the ridge is a no no where I live. I'm therefore looking to exhaust all novel / practical space saving methods in order to maximise the floor to ceiling height. 

 

The beam span (between the load bearing party walls would be about 5.1m for the rear dormer and 3.4m for the outrigger dormer. Depth of rear dormer (from ridge line) is about 3m. Depth of outrigger is about 4.6m. I've attached a couple of drawings.

 

Some of the things I've been thinking about include:

- side slinging / underslung joists 

- timber t beam joists / steel web joists with longer spans to reduce number of steel beams

- recessing steel beams into notches in existing ceiling joists and reattaching to new beamd

- smaller 3" steel beams + shorter joist spans

- supafoil over roof joists + minimal insulation btw roof joists to reduce joist depth

 

Is there anything else I should think about? I've held off engaging a SE just yet. 

 

Quietly hoping that @Gus Potter reads this post!

 

 

Hoping to meet and chat with lots of like minded people. Thanks!

[Marvin]

Hi @sylvane

 

Welcome

 

Bit concerned that you will find it difficult to convince Building Control that thinner insulation will pass the requirements.  What's the width of the bedroom?

[sylvane]

Hi Marvin,

 

The width of the room is about 5m.

 

The initial research I did seemed to imply that with a multifoil insulation over the roof joists, I might be able to reduce the thickness of the internal insulation between the roof joists. I need to double check if it could meet the new PT L requirement of no more than 0.15W/m2.

 

Given that the beams are going to dictate the floor level, I'm looking to see what the smallest size is for the 5m span.

 

Regards,

 

Sylvane