Loft Conversion - Rough Ideas

Loft Conversion - Rough Ideas

Author
Discussion

paulrockliffe

Original Poster:

15,707 posts

227 months

Thursday 6th November 2014
quotequote all
I'm hoping to conver my loft at some point in the future, years rather than months I suspect. I'm hoping to be able to DIY it as much as possible and want to avoid costly things such as steels, cranes and taking the roof off. I particularly don't want to mess around with the roof too much as if I can keep the work inside I can work on it slowly when I have time, rather than having to rush to get it back water-tight.

I'd like to get a design worked out though so I can get a working plan in place, I will likely sort out the new floor next year and this needs to be done in a way that is compatible with the rest of the structural work.

Standard detached roof with two gable walls, area is roughly 6m between gables and 10m front to back. Current roof is something like 4 x 2 rafters, with 2 purlins (something like 9 x 3) each side, ridge board and a King truss in the middle. The king truss bit has a large joist at floor level and diagonals from the ends of this to the ridge and triangulation in the middle.

My rough plan is to build a new floor at the level of the joist on the king truss, spanning between and to replace the internal diagonals with a vertical and a horizontal restraint and to then use the king truss as an internal wall between a bedroom on one side and the stairs and a bathroom on the other. I would tie the floor into the rafters to further restrain the roof from spreading.

Vertical dwarf wall to support the lower purlin at the front of the house, with possible roof lights between the purlins.

Collars towards the ridge line to triangulate the roof up top.

I'd like to add a dormer to the rear, though this will require both of the purlins to be cut. Likely two dormers, one either side of the king truss. I would support the lower purlin with a dwarf wall to transfer load to the floor and then to the walls. I'm stuck on the support for the upper purlin.

My brother is a civil engineer and can sort out all the structural calcs, but I want some rough advice before I start measuring everything and CADing the existing structure up.

Questions:

In an ideal world I'd get rid of the king truss, but this isn't going to be possible without major structural work is it? Would it be possible to remove the internal diagonal supports entirely, leaving just the vertical post and the triangulation around it if the rest fo the roof is sufficiently beefed up?

Can I design the dormer so that it transmits all of it's load to the floor and adds minimal loading to the existing roof?

How should the upper purlin be supported? Would it be possible to remove entirely by doubling up the rafters?

Feel free to tell me why my ideas won't work, I have a reasonable understanding of the mechanics and the terminology, but I might have misssed something glaring! I'm not about to start hacking about with anything, just pulling ideas together before I start trying to firm up a design.

Ta.

Gtom

1,610 posts

132 months

Thursday 6th November 2014
quotequote all
I'm coming to the of a loft conversion now for someone. Detached house with two gable walls. It's had a 254x146 steel at ridge level (well just below with a structural stud wall on top) to carry the ridge and dormer flat room and two 203x102 steels to carry the floor joists. There has also been two 315x115 glulam beams gone in aswell to carry the front of the roof.

Although steels can be spliced don't under estimate how heavy and difficult the are to fit if you don't want a crane!

This one I'm on will come in at around 40k but I have also stripped off to brick all the first floor and insulated and boarded this.

paulwirral

3,137 posts

135 months

Thursday 6th November 2014
quotequote all
I'd be asking about building regs first , you may have to use steel due to fire regulations , I did on a property in Sunderland .
And if that's the case you'll be able to position floor levels and dormers where you want , instead of forever looking and thinking " wish I'd put the steel in "

paulrockliffe

Original Poster:

15,707 posts

227 months

Thursday 6th November 2014
quotequote all
Gtom said:
I'm coming to the of a loft conversion now for someone. Detached house with two gable walls. It's had a 254x146 steel at ridge level (well just below with a structural stud wall on top) to carry the ridge and dormer flat room and two 203x102 steels to carry the floor joists. There has also been two 315x115 glulam beams gone in aswell to carry the front of the roof.

Although steels can be spliced don't under estimate how heavy and difficult the are to fit if you don't want a crane!

This one I'm on will come in at around 40k but I have also stripped off to brick all the first floor and insulated and boarded this.
Can I ask a bit more about why you used those steels? What was the structural support for the roof that you removed that necesitated the steel at the roof? And was it not possible to do the floor without the steels? Is it that it's the only way, or is there an element of it working out cheaper for your clients because the steel/crane costs are offset by savings in labour and/or more straightofrward structural calcs?

Without doing any calculations at this stage, that steel arrangement would seem disproportionate to the size of the additional loads caused by the weight of insulation and plasterboard and the need to support a cut purlin.

Labour is cheap for me if I can dothings myself, so I'd rather a more convoluted solution that allows me to do more myself and as I said, my I have access to structural calcs at no cost too.

Steels would be difficult to crane in due to a chimney breat on one side and next door's hose and overhead wires on the other. I have access to the tops of both leaves of the wall front and back, as well as a central wall and can fix a wall-plate to the gable walls, so I was hoping to be able to use wood only in the floor and to transfer pretty much all the weight of the insulation, plasterboard and associated structure to support them directly to the floor, rather than hanging them off the existing ceiling.

Is what I propose possible?

paulrockliffe

Original Poster:

15,707 posts

227 months

Thursday 6th November 2014
quotequote all
paulwirral said:
I'd be asking about building regs first , you may have to use steel due to fire regulations , I did on a property in Sunderland .
And if that's the case you'll be able to position floor levels and dormers where you want , instead of forever looking and thinking " wish I'd put the steel in "
I have looked at fire regulations before, I think the requirement is for 30mins protection for the new structure, which can be achieved by over-boarding the ceilings below.

When I researched it, I came across an example where a 22mm chipboard floor had satisfied building control, though that sits above the structural joists etc, so I'm not sure exactly how that was OK. I think I would be aiming to effectively over-board the ceiling above the existing ceiling joists, before fitting the new floor as the most straighforward way of achieving fire protection for the new floor structure.

paulwirral

3,137 posts

135 months

Thursday 6th November 2014
quotequote all
The steel beams I used were cut in half and had flanges welded to the ends so we could bolt them together , no cranes and half the weight to work with , could be an option but this was ten years ago , regs may have changed since .

Wombat3

12,162 posts

206 months

Thursday 6th November 2014
quotequote all
Had a loft conversion done last year including a rear dormer that runs pretty much the whole width of the house. There are 6 or 7 bits of steel in it including two that span the entire width of the house - one at the top as a ridge beam which is embedded in the wall at one end & supported by a central post and another at the other end (I did a hip-gable end conversion on one side). The second supports the dormer wall and one end of some of the floor joists.

Gtom

1,610 posts

132 months

Thursday 6th November 2014
quotequote all


This is what I have done although the ridge beam is under the ridge now and the the sistered purlins are now 315x115 glulams.

I dropped the ceiling heights in the bedrooms below because we gained another 450mm of height which gained a lot of extra space.

aberdeeneuan

1,345 posts

178 months

Thursday 6th November 2014
quotequote all
We had steels in ours and new joists placed on top of that to support the new floor. From memory, there is one either side of the house on which the whole thing is suspended but it was a few years ago now.

Key things with lofts are to work our what the space is used for. If it's a bedroom, hanging space is usually a challenge. Do you want a bathroom up there? Need to look at how to get the wastes connected up. We were lucky in that the services were directly on top of existing so it was easy (therefore cheaper).

Don't scrimp on insulation. Put some network points in there as your wireless may not reach. Storage in the rest of the house is a consideration - what are you going to do with the stuff that's in the loft. And try and get the stairs in so that they feel like they have always been there rather than an add on.

paulrockliffe

Original Poster:

15,707 posts

227 months

Thursday 6th November 2014
quotequote all
aberdeeneuan said:
We had steels in ours and new joists placed on top of that to support the new floor. From memory, there is one either side of the house on which the whole thing is suspended but it was a few years ago now.

Key things with lofts are to work our what the space is used for. If it's a bedroom, hanging space is usually a challenge. Do you want a bathroom up there? Need to look at how to get the wastes connected up. We were lucky in that the services were directly on top of existing so it was easy (therefore cheaper).

Don't scrimp on insulation. Put some network points in there as your wireless may not reach. Storage in the rest of the house is a consideration - what are you going to do with the stuff that's in the loft. And try and get the stairs in so that they feel like they have always been there rather than an add on.
Luckily, the things you mention are relatively straightforward. We'd be aiming for a bedroom and ensuite and if the king truss stays where it is we'd end up with roughly the bedroom in one half, then the bathroom in half of the other half and the stairs coming up in the remaining quarter. Where the stairs come up there would be room for a walk-in wardrobe or similar hanging space.

It's pretty much empty up there now and we'd have enough space under the eaves for most of what's up there, we're lucky in that we have a lot of storage space outside in the workshop if required.

We have a vent stack by one corner that would take the waste or at the other side of the house it can be wrapped around to the existing bathroom waste, so that's covered. I also made provisions for hot and cold water and central heating when I I was sorting that out last year. I've run cabling for TV, satellite, internet and the fire detection system up there already and when we had our rewire done I added lighting and socket circuits to the loft as well as a suitable cable for an electric shower, so that side of it is farily well covered. Only issue is that the current aeriel is inside the loft, so would need to be moved, but I ran a longer cable up there for that too.

We have a fairly decent sized landing, that housed the bathroom (in a cupboard!) when we moved in, so that should give space for the stairs fairly well. It's tight on length because the ceilings are high, but I think it just about goes. Headroom is good as it's pretty much under the ridge and there are a few options to get the rise into the available space.


Triumph Man

8,691 posts

168 months

Thursday 6th November 2014
quotequote all
Please also remember escape requirements. You will have to provide a protected means of escape all the way from the loft to the escape at ground floor level. This will have to achieve 30 minutes fire resistance (either achievable with blockwork and skim, or timber stud wall with 12.5mm plasterboard and skim to either side). It might be that your existing landing or chosen protected route already has this construction. You will however need 30 minute fire resisting fire doors (not required on the bathroom if this is on the route). You will also need to extend fire detection to the new loft room.

Please tell me if I'm teaching granny to suck eggs here, but you also cannot discharge the attic stair into a bedroom (or at least call it that on the Building Regs drawings...) as that is discharging into an "inner room" and is not permitted.

Lastly, if you do discharge the attic stair into what would have been a bedroom (which can sometimes be called a "Dressing room"), check at least one window in that room is suitable for "secondary means of escape" That is to say that if you cannot get out the front door, you can get out the window. Min dimensions are 450mm wide clear opening and an area of 0.33m2.


Hope that helps, ignore me if you've already got it covered!

ETA: One other point about protected routes, if you have one of these houses (like mine) where the stairs from first to ground discharge into an open living room, you will need to enclose them. Construction methods mentioned above will be acceptable.

Edited by Triumph Man on Thursday 6th November 16:24

Little Lofty

3,290 posts

151 months

Thursday 6th November 2014
quotequote all
You definitely want to remove the king post. Two steels at floor level should be enough, spliced into three sections they can be man handled into the loft and bolted together, no need for a crane. If you add a dormer a smaller beam at ridge level will probably be required. I'm guessing they'll cost around £400 per beam. You will use smaller timbers for the floor so saving money and headroom, I've converted lofts using huge timbers to form a load bearing floor and the cost saving is negligible, and its easier to get a few steel beams up than it it dozens of over size timbers. Getting the stairs right is crucial to making the loft work, and as mentioned you need to think about fire protection and means of escape. I'm not that far away from you if you ever want someone to cast on eye over it for you, I'm not touting for work as I don't do lofts anymore smile

paulrockliffe

Original Poster:

15,707 posts

227 months

Thursday 6th November 2014
quotequote all
Triumph Man said:
Please also remember escape requirements. You will have to provide a protected means of escape all the way from the loft to the escape at ground floor level. This will have to achieve 30 minutes fire resistance (either achievable with blockwork and skim, or timber stud wall with 12.5mm plasterboard and skim to either side). It might be that your existing landing or chosen protected route already has this construction. You will however need 30 minute fire resisting fire doors (not required on the bathroom if this is on the route). You will also need to extend fire detection to the new loft room.

Please tell me if I'm teaching granny to suck eggs here, but you also cannot discharge the attic stair into a bedroom (or at least call it that on the Building Regs drawings...) as that is discharging into an "inner room" and is not permitted.

Lastly, if you do discharge the attic stair into what would have been a bedroom (which can sometimes be called a "Dressing room"), check at least one window in that room is suitable for "secondary means of escape" That is to say that if you cannot get out the front door, you can get out the window. Min dimensions are 450mm wide clear opening and an area of 0.33m2.


Hope that helps, ignore me if you've already got it covered!

ETA: One other point about protected routes, if you have one of these houses (like mine) where the stairs from first to ground discharge into an open living room, you will need to enclose them. Construction methods mentioned above will be acceptable.

Edited by Triumph Man on Thursday 6th November 16:24
Hello, the stairs drop to a landing, the existing stairs are enclosed down to an entrance hallway that leads to the front door. I think there's 5 doors to upgrade, this will be a total pain as the linings are to rout out in situ and matching doors aren't cheap. I've read the regulations in detail trying to find an alternative and was hoping that the trend for relaxing the requirements might have continued. I've got smoke or heat detection in every room and both halway and landing and that's already been extended to the loft. To my mind my setup is a better option than the protected corridor and the minimum requirement for fire detection, but it's not my specialist subject.

Considering an escape ladder from the dormer, but I can't remember if there was a reason I couldn't do that off the top of my head.

FBP1

500 posts

149 months

Thursday 6th November 2014
quotequote all
We're most of the way through a loft conversion right now. We are going putting two bedrooms and a bathroom up there with 3 zinc clad dormers on the back roof - one central one for height over the stairs, and one either side for each bedroom. we're not allowed a big box dormer as we're in a conservation area.A conservation velux in the front roof for light into the central bathroom opposite the stairs.

Its a terraced double fronted Victorian house with a central hall arrangement and rooms either side with spine walls that run up to ceiling height on the first floor. It has a plan of circa 10m x 8m and an internal ridge height of circa 2.5m. So a similar shape in that it effectively has two gable ends with a ridge inbetween.

It has the older style roof arrangement with a ridge beam, but no king posts; just diagonal supports every couple of metres from the centre of the floor up to the one purlin beam on each side.

That arrangement has been replaced by a spliced steel beam underneath the existing ridge beam and doubled up rafters to support the dormers running from the ridge down over the new low dwarf/eaves wall frames and down on to the wall plate.

The floor is being supported on new larger joists that span the wall plates front and rear and which are unattached to the ceiling downstairs which continues to be supported by the original joists which are now carrying nothing else.

The fire thing is interesting as our architect is adamant that mains linked fire/smoke alarms plus intumescent paint/seals on the existing victorian panelled doors adjoining the existing hall/landing as well as the new floor will meet fire regs despite the new stairs not being enclosed (which would be good not to have to replace all 11 of the boogers...). apparently you don't need those chain closers like you used to now.

Having said that my kids will be up there so both bedrooms will have one of those fire 'rope" ladders installed and they will be shown how to use it. At the back there will be a one storey drop onto a garden room zinc roof so it shouldn't be too bad

Little Lofty

3,290 posts

151 months

Thursday 6th November 2014
quotequote all
Most building inspectors accept intumescent paint and seals on existing doors, it can depend on how thick the panels are and how well they fit. Some require lath and plaster walls on the escape route to be upgraded too, it's not an exact science unfortunately and is down to the individual inspector a lot of the time. Retro fitting fire doors into existing frames is a pita, but can be done with the aid of a small router, 35mm thick fire doors are available but only in limited sizes and styles:
Bit of info here on existing doors:
http://www.whitehorsedc.gov.uk/vale/guidancenote-a...

Edited by Little Lofty on Thursday 6th November 20:24

paulrockliffe

Original Poster:

15,707 posts

227 months

Thursday 6th November 2014
quotequote all
That’s interesting, so you've doubled up the rafters and fitted a steel at ridge level and that’s allowed you to remove purlins and all the other supports? That could be a workable solution if I can find a way to fix the steel at the end where the chimney is. Anyone any ideas?

Was that installed without taking the roof off?

Unfortunately our house is all exposed wood, so intumescent paint wouldn't work unless it was clear. However that link suggests that our 35mm doors would be OK with just the glazing downstairs being upgraded to wired glass (ugly but I could live with it) as we have a fire detection in every room and escape windows to the three bedrooms that are off the landing. I really should have specced the frames for 40mm doors in the first place to make this much easier!

What’s the current state of play with fire escapes? Could a Juliet balcony and spiral staircase for example be used to mitigate?

Little Lofty

3,290 posts

151 months

Thursday 6th November 2014
quotequote all
You can use intumescent varnish but it's more like treacle than varnish. Fire rated glass doesn't need to be wired, you can get clear glass but it is pretty expensive. You don't need a fire escape from the loft, that's what the protected route is for.

Alucidnation

16,810 posts

170 months

Friday 7th November 2014
quotequote all
Hate to be rude OP, but to me it seems you haven't got a clue what you are doing.

I suggest you get some proper plans drawn up by a decent architect and go from there.

Spudler

3,985 posts

196 months

Friday 7th November 2014
quotequote all
Alucidnation said:
OP,you haven't got a clue what you are doing.

get some proper plans drawn up by a decent architect and go from there.
This, end of.


paulrockliffe

Original Poster:

15,707 posts

227 months

Friday 7th November 2014
quotequote all
Thanks for the vote of confidence!

I'm fairly well aware of what I do know and what I don't know. I've read enough to understand the mechanics of the existing roof structure and what everything is there for, I've enough knowledge to design a structure that will have something in place to resist all the forces on the roof, but I don't have the knowledge to know how big those forces are or to calculate what size any particular element needs to be or how to work out what the most appropriate design is in terms of the space created, cost of materials and ease of construction.

I don't know whether it's normally sufficient to tranfer a lot of the weight to the new floor and whether this loading would normally be transmitted to two walls or all four. I don't know whether a single brick spine wall is usually sufficiently strong to be used to transmit load to the foundations, or whether I should take all the loading to the outside walls. I don't really know where to start with dynamic loads. I know that fundamentally with large enough timber, sufficient lateral restraint and the triangular shape of the roof a design with no internal support would work, but I don't know whether that would add too much weight to the walls and foundations.

I was really after some general pointers and information about what's normally OK in a normal house of my size and roof design. And pointers towards anything I might not be aware of, things to think about, especially solutions to cutting a purlin as without that there's no dormer and then things become a lot simpler, if not as good an outcome as we'd like. I don't know whether it's feasible to increase the size of the rafters sufficiently to remove the purlin or how you would normally then replicate the other functions of the purlin.

I'd like to be better informed so I can weigh up the cost and difficulty of installing steels against any alternative options. I didn't ask too much about Building Regs issues as I've already read all the regulations that would apply and know that there's nothing insurmountable in them, even if I haven't established all the details as yet.

This isn't something I can mess up as any solution has to be justified to BC, which will obviously involve a professionally qualified person doing the right maths and necessary alterations to the design on the way. I don't agree that asking questions and trying to understand the problem is a bad thing and I should automatically reach for the expensive professional who may or or may not design a solution that is quick and easy to install rather than something that better fits my circumstances?

Because my brother is able to do the calcs for me, I'd prefer to be able to CAD up a few options that I know I can install and that I know are likely to be viable for him so he can tell me what size timber to use where and make changes, rather than asking him to work off a blank canvas and using up more of his spare time. When I get to that stage I'll post some pics here and you can rip them to pieces if you want.

I'm always happy to listen to people that know better and take advice onboard.