How to build a loft floor (STRONG)

if you live in a traditional property in the UK you may be wondering how to board out your Loft in this video I'm going to show you the structurally sound way of doing it because it does not involve placing the Loft boards directly onto your ceiling joist it requires additional structural work which you might well be able to do yourself as a DIY project this is a traditional cut rafter roof for a property in the UK we can see here that we've got purlins running underneath that mid-span of the rafters we've got floor binders putting the Span in half of the ceiling joists and we have the ceiling joists spanning from wall to wall and in this particular case we have a internal load bearing wall underneath which is supported right down to ground floor so if you have that kind of setup it's quite easy to provide yourself with some storage space within the Loft and what most people do is they do a DIY project and put Timber straight on these ceiling joists now most of the time ceiling joists are not designed to hold that kind of weight and what you may get is cracking in the ceiling underneath so in the rooms below the ceiling may start to crack particularly if you've been up there accessing it and storing boxes of files and papers and heavy things like that now we need to convert something like this is by putting additional floor joists in so if we just take the cut away from this virtual model and we'll move it back slightly we can see that in this particular example so this side of the property I've left the Loft as it would be before any conversion work and in the other side we can see that a loft conversion is in progress so looking at this traditional cut rafter roof one thing that we can do is put Timbers from this load bearing wall here to the Gable wall there so that will look something like this the joists will be on joist hangers or a wall plate bolted to that wall and they will then come right over here and sit on this wall and they will be over the top of the existing ceiling joists but what we need to do is move them up slightly I'm going to go about 25 millimeters so that when they deflect it's not going to affect the ceiling below so that's your first option and you would then need to put a wall plate on here or build the wall up a little bit further in order to support that Timber and these Timbers would be spaced out probably 450 millimeters or something like that along the width of your Loft so that's a perfectly reasonable way of forming a loft conversion for storage as I said don't put your boards directly onto the existing joists them on some joists that have been designed for the particular span that we have in mind I've created here a useful little program it's an Excel spreadsheet where we can put in the details that we need for the floor so first of all if we just measure the length of the floor joists that we need from the point at which it is supported at each end just put that in here select whether it's a loft floor with or without stud partitions so that's a stud work wall so this one's without partitions we're going to use the lower grade of Timber c16 Timber spacing we had 450 millimeters so if you measure from one edge of the Timber to the same Edge on the other side don't don't measure in between because what we really want to do is go from Center Line of the Timber to the center line but the easier way is to go from Outer Edge to Inner Edge 450 millimeters and then we can select can play around here with Timber sizes whatever we can get hold of at the timber merchants and we can see here whether it passes or fails so in this particular example a 38 by 175 if you can even get hold of that size but just as an example the fails in bending stress and in deflection and the depth to breadth ratio is okay but the overall result this is what to look out for is a fail and it gives you some examples here of what to do about this so try a higher Timber grade closer spacing or larger section size and try increasing the section depth or closer spacing so what I'm going to do is make this a 50 wide by 175 at 450 centers V16 so if you want to get hold of that spreadsheet just go to robindyong.com and it's there as a download on the website or use the link in the description below that's freely available so having designed your floor joists you can now board it out now what people usually do to buy these packs of Loft boards which come in packs of three or so and the dimensions are something like 12 0 millimeters by 300 wide now you can see here that obviously we can't place them that way so we install them this way but the usual spacing for floor joists in a loft is going to be something like 400 450. or even 300 wide because what we're trying to do is generally keep the depth of the floor joists to minimum now these boards are designed for a trust rafter conversion not a loft conversion if you've got a traditional property let me show you this on the other side so here what we've done is a off conversion so this is going to be habitable space and the joists have been put next to the original ceiling joists so that we can use the depth of the floor like that and that's why usually we've got spacing of around about 400 to 450 because that's what the original ceiling joists space down so then if we use these boards you're going to get an overhang and structurally that's a bad idea so if we put another one next to this and we stagger them out we can see that there's no easy way of properly picking up the edges of these boards so what we're going to want to have is for the boards for the edges to sit on the floor joists the problem is with these is that they can't lever over for such a distance that it would make it a great waste if we would have to cut piece just there so really they're just not suitable for this kind of conversion unless you have a spacing of your floor joists at 600 millimeters because if you have them at 600 millimeters there'd be one here one in the middle and one at the end now coming back to The Loft floor calculator if we change this to 600 just look at what happens these joists Now fail and we're going to have to go for a deeper section in order for that to pass again right so you wouldn't out of choice for this kind of Loft go for a spacing of 600 millimeters we'd go for something like 450 either to match the existing ceiling joists and to put the new joists in between or as we saw on the other side of the building to space them perpendicular but to make it economical so if we were to if we were to decrease the spacing so let's say we have our new joists at measure this at around about 350. so change that to 350. we can probably now drop right down to 150 millimeter depth right so at 350 spacing we were able to get 150 depth at 450 we were able to get it at 175 depth but if we increase it to 600 then all of that fails and we need to increase it to a rather large joist of 200 deep now this spreadsheet has been designed with the lowest possible weight on it because these Loft floor joists are not going to have a lot of weight on it so it's a very economical calculator spreadsheet to have as I said do please download that so what do we do well if possible if you can get these up the Loft hatch use a loft Board of 2.4 meters by 600 so that is cut from a normal sheet of plywood OSB or chipboard a normal sheet is 2.4 meters by 1.2 so these come in sizes of 2.4 by 600 wide so 600 millimeters hopefully go through your Loft hatch and we lay these out perpendicular to the floor and you can see now that this goes across a lot of joists so that the overhang here now is not much of an issue even if we cut the timber so what we're going to do is we're going to put this in up against the binder we're going to put a new joist in next to the binder because we don't want to load the existing ceiling at all and then we're going to cut it at that point there so we'll cut that away and then the next piece will go against it so let's just turn that around and this is a piece of Rudy cut in half what we're going to do is create a brick bond pattern the next sheet is going to go as a half sheet and then we're going to have a full one and then we're going to have halfway against and so on so what we'd probably do here is just move this joist over a little bit to pick up that edge so that's the kind of so that's the kind of thing we need to do it's a brick bond pattern all the edges are picked up with a joist and of course it's well nailed down or screwed down to each joist the joists are supported on the wall here the Gable and on an internal load-bearing wall will make sure first of all that that wall goes down all the way to foundation and if it's got joists sitting on it already so floor joists and in this case it's got purlins sitting on it it's going to be a load-bearing wall but of course for any kind of Loft conversion do get a structural engineer involved I'm not just saying that because I am a structural engineer I'm saying that because I do inspect a lot of properties and often there are Loft conversions that don't have building regulation approval and then it can be very difficult to sell those properties without a lot of Hassle and delay once it comes to selling your property in the future so do please download The Loft floor calculator which I've provided for free on my website robindyong.com and please let me know in the comments whether you like the calculator and what other topics you'd like me to cover in these videos

Channel: Robin de Jongh

Views: 90,648

Keywords: how to build a loft floor, how to floor a loft uk, how to floor a loft over insulation, how to floor attic, loft floor installation, loft floor boards installation, how to board a loft, how to board a loft for storage, loft conversion uk, diy loft conversion uk, loft conversion, diy loft conversion, attic storage, robin de jongh, how to board a loft without loft legs, build it with rob, diy loft, loft conversion structure, loft storage, strengthen loft floor

Id: lHLDH55Igc4

Length: 12min 5sec (725 seconds)

Published: Fri Feb 03 2023