Loft ceiling height

[p.lavers]

I am thinking about a loft conversion in a victorian terraced house, but have only 2.20 meters of max head room (from top of 3" Joists to bottom of ridge beam).

I have heard mention of using solid self-supporting wood flooring without joists. Has anyone any information on this - suppliers etc. The span will be about 3m from front of house to central structural wall.

Anyone have any ideas on saving headroom at the ceiling end - eg ultra thin insulation?

I would like to build a dormer at the back of the house. How much headroom is this going to cost? Are there any good ways of increasing head room here? I have thought of using a roof dome and upstand. Can this project above the roofline without planning consent?

Many thanks

[Staffbull]

One thing I am sure of is, no way can you project above the roofline without planning

[Christian McArdle]

We had a number of innovations in order to save headroom. We weren't as tight as you for space, but we wanted it to be the master bedroom but not have a claustrophobic effect (I'm reasonably tall at 6'2").

1. Firred dormer roof joists which reduce in size towards the eaves gives maximum headroom, flat ceiling and enough fall to the flat roof. Note that the bottom of these are actually higher than the bottom of the ridge beam, so the dormer ceiling height is a good 10cm higher than the actual apex, with a step up to accommodate it.
2. Stressed box construction where the flooring is plywood glued and screwed to the joists. The gluing and screwing enables to knock a good couple of inches off the required joist depth.
3. We used Triiso Super 9. This winter should show if it works or is snake oil. The next thinnest alternative is full fill Kingspan or similar with

25+12.5mm K17/K18 underboarding.

If you are really tight for space, you may be able to use steel joists instead of wood. This will be expensive and difficult to locate a willing builder. However, you can get suitable steel joists into the same space as the existing 3" ceiling joists and their small size means they might not be significantly heavier.

A stressed box construction will need to be designed by a structural engineer and approved by the BCO. For a 3m span, you may find that 4" joists and 18mm plywood is all you need.

Absolutely not, although planning permission might be realistically obtained if the protrusion is not visible from the street.

Christian.

[p.lavers]

Thanks for that. One thing I don't understand is:

Note that

How can the dormer ceiling height be higher than the apex without building above the roofline?

Cheers

[Christian McArdle]

The entire flat roof is thinner than the depth of the ridge beam, so the bottom of the roof joists are higher than the bottom of the ridge beam.

Christian.

[The Natural Philosopher]

Had me puzzled too...