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[Martin_1962]

Well the knowleage is here, what do you need to do for a loft coversion to a modern house?

[Kevin Wood]

The first question is how strong are the upstairs ceilings. I was lucky in that my house was built with that in mind. Loft floor is suspended by two great metal girders running the length of the house.

Kevin

[Marks DTM Calib]

Well the knowleage is here, what do you need to do for a loft coversion to a modern house?

Pretty strict these days.

Generally you dont need planning permission if only fitting sky lights, its different how ever if you are changing the roof line.

You will need full building control which covers a hell of a lot eg.

Fully insulated to lastest regs
Sound deadening now also a consideration
Structural i.e. floor joints rafters etc
Fire - Generally this requires fire doors on all floors which access onto the hall/landing etc!
Obviously wiring (another pointless reg set creating jobs for the boys!)


Quite considerable but, actually not that hard to achieve for most plus if you get a good building control officer (I didn;t for my extensions, he was rather useless!) then they often offer advice.

All the building regs are available on the web for free here:

http://www.planningportal.gov.uk/england/professionals/en/1115314110382.html

[Phil]

Basically a 'modern' house is likely to have a trussed rafter roof, and therefore loft conversion is not possible without completely replacing the roof.

[Marks DTM Calib]

Basically a 'modern' house is likely to have a trussed rafter roof, and therefore loft conversion is not possible without completely replacing the roof.

Not true, its actually reasonably easy to work around by using sister joists on the rafters with a notched ridge board and either installing RSJ's to sit new floor beams in/on or by again, sistering joists onto the existing ceiling joists.

Of course, the joists will have to be as defined in the span tables for such items in the building regs and it takes a reasonable level of carpentry to do but by no means impossible and often not much more involved than a stick bult roof where often the existing ceiling joists do not meet spec.

When I did my recent extension, I intentionally fitted flooring grade joists in the roof as the celing joists to give full load bearing capability. These were 250mm x 75mm (9x3 inch) for a 5 meter span at 400mm intervals.....real big buggers basically

[Phil]

Basically a 'modern' house is likely to have a trussed rafter roof, and therefore loft conversion is not possible without completely replacing the roof.

Not true, its actually reasonably easy to work around by using sister joists on the rafters with a notched ridge board and either installing RSJ's to sit new floor beams in/on or by again, sistering joists onto the existing ceiling joists.

Of course, the joists will have to be as defined in the span tables for such items in the building regs and it takes a reasonable level of carpentry to do but by no means impossible and often not much more involved than a stick bult roof where often the existing ceiling joists do not meet spec.

When I did my recent extension, I intentionally fitted flooring grade joists in the roof as the celing joists to give full load bearing capability. These were 250mm x 75mm (9x3 inch) for a 5 meter span at 450mm intervals.....real big buggers basically

A trussed rafter roof is a designed structure that transmits loads at specific points, they are made from very small section timber (ex 125 *38 generally) and if any of the timbers are removed and extra purlins and the like are installed then the amount of strengthening required to ensure the roof does not collapse (at time of alteration as well as after completion) makes it very expensive, plus if any work involving cutting of a trussed roof is going to be undertaken it needs to be checked by a structural engineer

A trussed rafter roof is different to a 'traditional' cut rafter roof

Oh and i have Part A of the building regs, and generally there is not a timber that will cover a single span of more than 4m, which depending on the load bearing walls (a modern house with a trussed rafter roof generally has no load bearing walls in the upper floors as they are not required) would mean going to an engineered beam, which with a min size of approx 200mm would considerably reduce head room

[Marks DTM Calib]

I think what your missing Phil is that the approach taken for conversion is to effectively replace the truss roof assembly by a traditional stick built roof by internal assembly, the only parts of the truss sections that remain are those which actually have the physical parts attached to them (i.e. the roofing battons and plaster board ceiling), the structual integrity is maintained by the full spec timbers which are sistered (connected to) along side these remaining truss sections.

The max flooring span is 6m in Part A, the max timber floor span for a standard beam is 5.1m at 400mm spacings using the 225 = 75mm structual timber as per the following guidance note:

http://www.rushcliffe.gov.uk/upload/public/attachments/39/TA006timberfloors.pdf

This is a standard recognised approach used to convert truss roofed buildings.

The other thing to be very aware of is that few, if any, of the houses built in the last 100 years will currently have ceiling joists installed which meet the requriements of a floor joist suitable for domestic loadings!

[Albert1]

You'll need to be able to access the loft "room" via fixed stairs - a ladder isn't allowed - so you need space on the first floor for the stair case to be installed.

[Marks DTM Calib]

You'll need to be able to access the loft "room" via fixed stairs - a ladder isn't allowed - so you need space on the first floor for the stair case to be installed.

Correct as its required to support a means of escape for a true loft conversion and hence the need for fire doors to allow the means of escape to not be blocked to the main exit.

This is also the loop hole that allows you to board and insulate your loft plus add a window to creat a non inhabitable room if the means of access (i.e. ladder) can be removed (which intheory indicates that it is not inhabitable!).

[Phil]

I think what your missing Phil is that the approach taken for conversion is to effectively replace the truss roof assembly by a traditional stick built roof by internal assembly, the only parts of the truss sections that remain are those which actually have the physical parts attached to them (i.e. the roofing battons and plaster board ceiling), the structual integrity is maintained by the full spec timbers which are sistered (connected to) along side these remaining truss sections.

The max flooring span is 6m in Part A, the max timber floor span for a standard beam is 5.1m at 400mm spacings using the 225 = 75mm structual timber as per the following guidance note:

http://www.rushcliffe.gov.uk/upload/public/attachments/39/TA006timberfloors.pdf

This is a standard recognised approach used to convert truss roofed buildings.

The other thing to be very aware of is that few, if any, of the houses built in the last 100 years will currently have ceiling joists installed which meet the requriements of a floor joist suitable for domestic loadings!

Thanks for the lesson in construction, i'm only the 3rd generation of my family to be involved in the building industry.

You made the point yourself (and confirmed my 1st post), a whole new roof is constructed alonside the old one, but in a Trussed Rafter Roof this work has to be done BEFORE any members are removed, making it very difficult to make cost effective due to restriced access and space in the roof void.

if you have a look here :- http://www.tra.org.uk/pdf_files/pds8.pdf it explains what you need to do in a trussed rafter roof.

The cost and difficulty of this work (especially if its a mid-terrace house) means it is 'in most cases' not economically viable

The steels/ timber needs to span from party wall to party wall to transfer the loads, because as stated before most 2nd floor walls are non load bearing in a 'modern house', again practically impossible in a mid-terrace house and at best difficult in an end terrace.

As i said dont get a traditional cut roof confused with a trussed rafter roof

[Phil]

You'll need to be able to access the loft "room" via fixed stairs - a ladder isn't allowed - so you need space on the first floor for the stair case to be installed.

Not technically correct.

A stair case should be at a pitch of approx 42 degrees, with a rise of approx 180mm and a going of 220mm and a clear headroom of 2m, generally this means you need 4m of 'horizontal' space to fit in the staircase

BUT if the space is restricted then you can have an alternate tread staircase which can go to a pitch iirc of 60 degrees and in effect becomes a 'fixed ladder' with a handrail (all set out in part K of the building regs).

[Richie London]

http://www.loftconversionguide.com/

[alexandjen]

Did mine about 5 years ago, full width dorma on the back with 2 Velux windows on the front.
2 bedrooms with a seperate cloakroom.
Building regs were bad enough then, I hate to think what It's like now.
All habitable rooms had to fitted with door closure devices, all new door were heavy duty fire doors with the fire strip (Intumescent)rebated into the edges.
Interlinked mains powered smoke alarms with battery back up on all floors.......one goes off, they all go off.
The first floor landing had to be boarded over the floor boards for fire regs.
Escape window, not lockable on the dorma - special hinge which allows the window to be opened at 90 degrees to the frame.
Escape Velux at low level on the front.
Masses of insulation in walls, roof and floor.
Independant floor joists spanning from front to back resting on the outer and inner supporting walls - 8 by 2 and a half inch timber if I remember correctly.
The list is endless..............