dormer construction

it is now time to open the roof and construct the dormer, unless you have a tin roof on your scaffold i would urge you to do this on a dry day!!! also before you open the roof, make sure your pad stones for are cast and ready to accept the rsj for the ridge.

most loft conversions consist of a rear dormer, with this in mind we are only going to strip out the back section of the roof, this is quite straight forward, just remember to prop up the rest of the roof before you start cutting out struts, purl-ins and rafters. when the section of roof is removed install this final steel, normally directly underneath the existing ridge.

the timber work for a dormer construction is usually completed in a day, it is advisable at this stage of a loft conversion to have a professional roofer on hand to help keep the property water tight. construct the dormer walls in the same way you would construct a stud wall remembering double timbers round doors and windows.  once  the walls are up we can now put on the flat roof of our loft conversion. bolt a timber into to rsj under the ridge, place jiffy hangers at 400mm centers on to this timber. now we are going to place 6x2 timbers into these jiffys across and onto the dormer wall running parallel.

to complete this stage of the loft conversion place firrings on top of the 6x2s, a layer of 100mm celotex and then deck the roof in 18mm OSB.

installing the floor joists to a loft conversion

now that the RSJs are in, we can start putting in the floor joists into the loft conversion. in each of the steels we are going to fix a length of timber, if the steel fabricator hasn't pre-drilled the steels, you must do this now with a mag-drill, a 14mm hole every 400mm centres. it's a good idea to mark out where your joists are positioned on the steel before you drill to avoid putting a hole where a joist will be. once the steels are drilled cut a timber to the required length, the timber should be slightly narrower than web of the steel and the same depth, for example if the internal measurement of the steel is 8" and the depth is 2" then you should use a 7x2 length of timber. place this timber into one of the floor steels clamp into position a mark out the drilled holes through the steel, then drill the timber with a 14mm bit. place the timber back into the steel and bolt together using M12 bolts, nuts and washers. repeat this process with the other floor steel.

we can now start installing the joists, if you haven't already done so mark out the position of the joists at 400mm centres. cut the first timber to the required length(the distance between the two steels) and fix either side using jiffy hangers and repeat with the remaining joists. remember to double up the joists where the stairs are going to be installed, and to treble up the joists under the dormer walls of our loft conversion. once the joists are in all that remains is the noggins cut and fix the noggins approximately every 1200mm, a good idea would to smear "grip-fill" on the joints where the noggin meets the joists, this will prevent any creaks on the floor. if you have any questions on this post, or need advise on a loft extension please send me an email.

installing the steel RSJs into a loft conversion

in most cases your new loft conversion will require the installation of RSJs. generally 3 RSJs are required, 2 large steels to take the weight of new floor, and a smaller steel to support the ridge. these steels are normally installed prior to any timber framing. the process starts with openings being made in the brickwork where the steels are going to be fitted. in each of these openings a concrete pad stone needs to be cast just below where the steels are going to sit. the hardest part of installing the steels in a loft conversion is getting them into position, the smaller steel for the ridge is not normally a problem but the 2 floor steels can be tricky. if possible craning the steels in is the easiest option but this can be expensive and if the scaffold has a tin roof it will not be possible to use a crane. if a crane isn't viable then man power and a couple of block and tackle's might be the answer. once the steels are in place on top of the pad stones you need to brick them in to stop them moving. you can now start timber framing the loft extension.