Loft Conversion - Rough Ideas
Discussion
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.
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 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?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.
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?
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. 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 "
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.
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.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.
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 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.
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.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
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.
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?
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?
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.
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.
Little Lofty said:
I'd have to disagree, with steel in place you can hang smaller timbers off the steel beam. As the steel shortens the span, the joists are smaller so will create more headroom not less. The OP states the house is 10m deep so each timber will have to span 5.0, ( that's assuming there is a load bearing wall in the centre of the house) this is on the limit for even a 225x50, 150x50 could be used if steel is used so giving an extra 75mm of headroom. This may or may not be critical, but no matter, steel will nearly always allow more headroom. Also depending on the roof detail it's not always possible to have a joist resting on the inner leaf as it may have to be cut on too great an angle, greatly reducing its strength.
OP, I know a guy who lives in Chester -Le- street would do your plans if your stuck, also with the greatest respect to your brother, some of the calcs I've seen for lofts are outrageously over the top, make sure the couple of hundred saved by not using a structural engineer familiar with lofts isn't eaten up by over the top timbers and steels.
Thanks that's useful. I'll measure the spans at some point and put a diagram up. I suspect they're closer to 4.5m and I'd think there's room to get the timber to the inner wall without mitring the top edge too much, from memory there's a good gap to the underside of the roof there, I tihnk you can get your head in it. I'd have guessed bigger timbers would be available than 225 x 50 though? OP, I know a guy who lives in Chester -Le- street would do your plans if your stuck, also with the greatest respect to your brother, some of the calcs I've seen for lofts are outrageously over the top, make sure the couple of hundred saved by not using a structural engineer familiar with lofts isn't eaten up by over the top timbers and steels.
The ground floor joists are 3" x 8" and span the same gap, though I appreciate the loading is different.
The spine wall in the middle of the house extends a little over half the width of the house, so I wondered if it was feasible to sister up the 8" x 3" joist that's part of the King Truss that extends front to back and is supported on the spine wall. From this I could then run run joists from this to the side of the house, these would all be a little under 3m wide. Would need a wall plate. Probably better with a diagram really.
Joists from front to back would be easier to support at the wall end, but would mean longer timbers. 5m might not be too far off the limit of what I can physically get in through the house. Would it be better to transfer load to all four walls or are the walls generally so over-engineered that it doesn’t really make much difference?
Steel wouldn't lower the floor height unless the king truss then came out because the floor will likely be raised to the height of the lower joist in this truss structure. Mind you, if a steel at apex level let me remove the king truss entirely without huge knock-on costs elsewhere it might be worth the cost as with the truss in place I'll end up with a smaller bedroom and a larger bathroom than I'd prefer.
You might be right regarding the level of calcs required, my brother designs commerical buildings, hospitals, bus stations etc, so I don't know how in tune he would be to the requirements of BC, but I would think I could get a list of everything they need to know and tailor his work to that. I'll bear your contact in mind when we get to that stage, though it may not be for quite a while!
I was going to measure up tonight as I've a free evening, but my girlfriends car conked out last night, so I'll be messing about with that instead.
Thanks, that's great!
I had a quick look earlier as I'm putting off going out in the cold to fix this car.
I think the issue with steels in the floor will be that to run them across the shorter length means removing that tie beambefore there's anything in to replace it. And the long length would require more steel and probably more than can be inserted without a crane.
The span from the tie beam across to the gable wall looks comfortable for wood rather than steel to my untrained eye.
If I can get a proper floor in first then it makes the rest much easier as I have something to prop the roof off while putting a steel in at ridge level and removing the king truss.
I had a quick look earlier as I'm putting off going out in the cold to fix this car.
I think the issue with steels in the floor will be that to run them across the shorter length means removing that tie beambefore there's anything in to replace it. And the long length would require more steel and probably more than can be inserted without a crane.
The span from the tie beam across to the gable wall looks comfortable for wood rather than steel to my untrained eye.
If I can get a proper floor in first then it makes the rest much easier as I have something to prop the roof off while putting a steel in at ridge level and removing the king truss.
Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff