Loft Conversion (hopefully)

[dinger541]

Hi all,

This is as usual just a fact finding message to see if what i want to do is both feasible and within the meagre costings i've got.

I'm planning a loft conversion with as much work done by myself as can be done. As per usual the experience level (both professional and amateur) within this hub will dictate the way that i go with this project.

First i've had a structural survey done with a view to stairs access and structural integrity (weight loading ) of the loft area, both were good.

The loft beams are 100mm deep, i believe that i need a 50mm airflow between the roof and the insulation but then i get a bit confused, various literature and other people have different views a to what sequence goes next.

I would like the easy option of 'Kingspan' type cladding 50 mm thick, foil backed plasterboard then loft room but i will bow to whatever other options that people in the forum have had.

As per usual i thank you all in advance

Dinger

 

[Hazelb]

My builders used a foil type sandwich of insulation. It had about 7 different layers ( not the one with just foil and air bubbles ). I think it was attched direcly to the rafters, so leaving an air gap behind. It was then plaster boarded.

 

[masona]

Doesn't matter what type of insulation but you must have at least 50mm air-flow at the back to provide circulation which mean you should have a few ridge tile vents at the top and at the bottom the air coming in from the soffit vents.

Do you know what size floor joists to use and how to support the roof?

 

[Thermo]

the foil type is tri iso 9. Its easy ish to put up if there are two of you, and looking at your roof it would be very quick. It comes in a big roll and you staple it to the rafters and then counterbatten it for the plasterboard.

The disadvantages are you have to faff arouind sealing the joints with tape, you cant screw into it as it all puckers up so you have to nail the battens (not a problem with a nail gun anyway, but if you come to screw in fittings such as shelves later it can be a pain if you drill too deep) and its about £200 a roll (20m2)

Having said that its quick and you dont need foil backed board as it does the job as well

 

[dinger541]

Thanks to all for the replies...

A couple of questions for you though... Im getting a wee bit of knowledge behind me after a couple of years of sustained DIY and from being in this forum.... that said i occasionally get very confused lol.

Masona first: As per usual good advice but, floor joists and support the roof, sorry mate need more information there?... the structural engineer says the joists are good enough for what we will use the room for ( a bedroom for a teenager, complete with iron bars and a cattle prod if i get my way!! ), the roof is a dorma structure, what you see is efectivly the tip of the house, the base of the triangle is the roof of the dorma and the ceiling of the two bedrooms below.

Any other bits of info you need, ive got me tape measure out mate...lol

Second to Thermo, the stuff your talking about is the silver foil i believe ive seen in screwfix... expensive but easy enough to do if needed. I was fixated on a Kingspan type of insulation, easy to fit ontobattons in the space between beams thus allowing the 50mm gap required but i'll go for anything thats easy. Is it just that across the beams (horozontally) and then plasterboard on top??

Thanks all again for the info

Dinger

 

[Mr Winston]

Stating the obvious - you will need to make a building regs application and should enquire with the planning dept if you need to make an application to planning as well (particularly if you are building a dormer roof).

The building regs application will need full structural details of what you have and what you intend to do. The easiest way is to get a surveyor to draw plans and specify everthing on the drawings - that way you can get approval from the council and know exactly what you need to do (rather than oing something and having it condemned by the BCO)

 

[claridge]

I agree with Mr winston... Looking at the photos I question whether your 'new floor to new ceiling height' is viable as a habitable room. Remember the floor has to be suspended free from the ceiling of the rooms below. The floor has to bear on supporting walls/steels. This brings the floor up....the rafters have to be packed up for the air flow as you have mentioned before.... bringing the ceiling down .....Can you still stand up

 

[masona]

Masona first: As per usual good advice but, floor joists and support the roof, sorry mate need more information there?... the structural engineer says the joists are good enough for what we will use the room for ( a bedroom for a teenager, complete with iron bars and a cattle prod if i get my way!! ), the roof is a dorma structure, what you see is efectivly the tip of the house, the base of the triangle is the roof of the dorma and the ceiling of the two bedrooms below.

You will almost certain need bigger ceiling joists which will be the new floor joist (most of the loft conversion I've done are 9"x3" joists onto the side of the ex- 4"x2" ceiling joists) or you may get away with a couple of RSJ's, without seeing it I can't say because you will need new upright studs from the floor area supporting the new purlins as well.