How to build a loft floor (STRONG) 

✅Get help with your loft conversion geni.us/loftsurvey

I'm from Germany. My wife and I own a former farm house which was originally build in 1923. The structure of the timbers carrying the roof is somewhat similar to what you displayed in this video. However the dimensions are quite different and certainly the standards applied to constructing such structures have changed a lot during the past century. I believe in the UK there are also a lot of historical buildings. I would be interested to see a video about how the craftmanship has changed in the UK during the past 100 years and how historical buildings compare to more modern structures in this regard. Your videos are very well illustrated and your clear speaking makes it easy to follow for foreigners like me not speaking english as their native idiom.

Many thanks Robin. As a property maintenance and repair professional, I can confirm, we are regularly are called to checks on floors, and carry out repairs to the junction of the floor sheeting, where it’s previously unsupported

Thankyou for the spreadsheet, very helpful and just what we needed.

This might be the most technical loft floor video ever made!

Your videos are amazing, in-depth clear and concise . thank you

Yes robin this is brilliant I am going to download this spread sheet calculator this is exactly what I need. keep these videos coming. Legend.

I really appreciated this. I live in a house built in 1907 which, by and large, is over-engineered. Part of the eaves have been converted into storage by being floor-boarded and I was horrified to find that the joists supporting the ceiling below the storage area are 3 inches by 1 1/2 inches. (Approx 75mm x 40mm). Naturally, there is some cracking on the lath and plaster ceiling. Having used your calculator, I now know exactly the dimensions I need to create a safe storage area which will not damage the ceiling. Thank you so much, Robin!

Excellent video, it's been a while since I've learned so much in such a short amount of time. Thank you!

I am a retired Carpenter/joiner and have worked in the residential sector all my working life.. In the very early days I was working on a loft conversion with a couple of guys.. they cleaned out all the rubbish between the existing 4" x 2" Joists in the loft and screw fixed additional 4" x 2" timbers on top at 90 degrees to create a lattice.. Every joist was screwed down to the one it passed over and it created an incredibly rigid floor.. I did not realise until a lot later that 'You cant do that..' became the response if I dared suggest this option.. Considering how succesful this option was it has always bothered me why literally no-one has looked into this as a construction method. The load spreading is incredible and I would love to hear an Engineers opinion..

Great video! Really appreciate you creating this. Thanks!

Just about to undertake adding some flooring into my loft eaves for box storage - I have a general idea but this has focused me a little more! I’ve watched a few YT vids but this is definitely the most useful. As a CAD engineer myself the CAD visuals were very helpful!

Thanks for the advice and videos

Fabulously well explained Robin. Calculator fabulous too 👍

Brilliant video mate

Dude...this is exactly what I'm looking for ...thanks ;-)

Hi Robin, great video explaining how to do it differently. Your CAD example is near identical to my loft, apart from a chimney breast on the party wall. We had a new roof on our 1950s house last week and I took the opportunity to ask the roofers to lift in twelve 6x2 joists up into my loft when they stripped the old roof, ready for me to crack on with in the coming weeks. Watch this space. (Liked and subbed) 👌

Thanks mate. Very useful 👌

Hi Robin, thanks for the videos. It would be great to see how you'd deal with some of these loft conversion concepts on a building with a hipped gable, like a 1930s semi. I'm wondering how to deal with the height constraint between the wall plate and the pitch of the roof when using timber beams or joists.

Hi Robin. Really enjoy your video's and have learnt a lot watching them. As far as I'm aware you as long as you glue the joints on t&g flooring it doesn't need to sit on a joist. Also you could set the joists at 400mm centres to make the 1200mm total

I would be interested in your views of loft legs and similar products.

I really appreciate your videos we are a young family on one wage trying to modernise a 50's semi and the info that you give out is invaluable to me I don't have people to ask. I'd love to ask how are you getting the large joists in do they have to go through the roof moving tiles I'm guessing because they can't be cut. Thank you

Never knew this. Ive partly boarded each house ive owned , straight onto ceiling joists just for storage . Not on my next house eh. What was a quick diy weekend job is now maybe quadrupled in price and time but the right way to go about it.

This is amazing, thank you so much. How important are the ceiling binders? My Victorian property has this exact arrangement but without the binders

Hi Robin great work! Is there a calculator which takes into account the what the span can be in the loft if you double or triple up joists and bolt together?

Good video

Any plan for basement videos or wind calculations.

Thanks for the detailed video! Can't fault your structural work :) However I do have some questions about the insulation, please. Modern building regs require a U-Value of 0.16 in England and Wales and Northern Ireland (for retrofit, it's higher for new build and in Scotland), so if the floor of the loft is insulated, then you need to leave space for that. The most common mineral wool (k value of 0.044) would require a depth of 270mm, plus the BBA recommends an air-gap of 50mm above that to allow air to flow from eave-to-eave, to prevent condensation forming on the bottom of the boards. So, just as a suggestion, perhaps either your calculator tool should have a minimum height of 220mm, or if someone wants less than that, there could be a warning flag up to say that a higher grade of insulation is required or that under-rafter insulation should be used instead, to make it a warm loft with the eaves sealed? What do you think? Cheers :)

Hi grate video would love to see how u would do the floor with out a supporting wall in the middle but a 12 by 3 beam from frunt to dack

Hi Robin great explanation and thanks for the download of the span table. I have a quick question please if I may. Can I retro fit a build in joist hanger by cutting a slot into the brickwork and tapping it in? I’m struggling to get 100mm face fix Joist hangers without paying a silly amount of shipping. Thanks for the help 👍🏻

Great video……im thinking of doing this…..however, how would you fix those hangers to thermolite brick? It crumbles so easily.

Thanks Robin. Great video and easy to understand. I am curious to ask if there should be a gap for ventilation between new insulation and new boards? Many thanks.

Having an overhang on a board beyond the edge of a loft floor joist is not necessarily a critical point of weakness IF the loft area is intended for low loads/usage, (only storage and occasional access) AND if, (as you have indicated) the boards are bonded/staggered IF relatively narrow, (eg. 300mm) tounge and groove boards are used since the overhanging board will be supported by the tongue and grooves of the adjacent staggered boards.

Great video thank you. Got the calculator but widths etc are fixed. Most of timber places sell for example are 45 or 47mm width but the sheet has 50mm. Is it ok using the 50 for those instances as you cant put exact. Also if i fitted a wall plate to stone wall at one side am i best adding joist hangers to face or just sit the joist on the top of the plate? The wall plate would be fastened with decent sized frame screws at multiple points along it. Thank you. 👍

Hi I have question - I have loft with 3 angled roof and 2 floor binders are very close to the middle and spaced about 1 m away from each other and sealing joists are nailed to the roof joists and not on the outer walls bricks. It looks like the wall are about 0.5m away from the point where floor joists are joined to the roof joists. Thank You

If the end wall is constructed with a Thurmolite type block work, what’s best joist hangers or fix a timber joist to the wall? What is the required of a fixing medium?

Great video buddy and thanks for the calculator. So if I want to create some storage for static loads like Christmas decorations, and other bits, should I still hang some joists off the shared party wall to external wall of my semi-detached house?

Can the joists sit in brackets/hangers on both sides of the wall or do they have to be supported by a wall on 1 side?

At 7:11... the way the run the 2x8s and double them ...if you put two 2x4s stacked on top of each other to get a 2x8 then doubled that stack and put them side by side then stapped them with metal plates to keep them together... would it have the same strength and be able to handle the spans?

do you have any calculator for calculating I beam steel gable to gable ? thanks. not a builder just trying to price up materials for my house

You mentioned a few times that it will good fo storage but would this conversion be suited if you were converting it to an additional bedroom?

Robin what is the software you are using in this video?

6:15 do you have video about how to do flooring for this kind of loft? The Truss one, I have exactly like in this video from that time stamp

Hi Robin, very informative series of videos. For light storage is it possible to use the ceiling binders to support 3m 2x6 timbers, as the binders are themselves supported on internal wall & party wall?

Im Semi detached and have only 1 wall to attach hangers too. Is there a main beam on the other side that can support the weight?

I’m from the Philippines. What is the best material for loft flooring? Our contractor is planning to use 3/4 inch plastic panel instead of marine plywood. Will it last and is it safe?

Hi Robin, all very helpful. Thank you. I am however thinking about the practicalities of foing this sort of job when dealing with an existing loft. The only way to take long timbers in a loft is through a loft hatch. This makes the task impossible if we want to keep those long timbers all in one piece because there won't just be enough space. So, would it be possible to cut timbers, say, in halves and then put them together somehow once in the loft? How could the timbers be put together again in a structurally safe way?

Can I ask what loft floor joist would you use for 270mm, 300mm clearance for insulation and

After you nailing the new joists into the wall? Or they can just hang on top of the old joist??

I have seen on other videos suggesting to install Loft Leg directly on the joists and then floor boards on top of them. My question is why can't we install floor boards directly without addional joists? its on new build houses?

Do you fill the bottom with insulation or not before you put boards in there ??

Hi Robin, excellent presentation! What software are you using?

Excellent details on practical solutions to real life situations to multiple variables no matter where you live. I am a retired Canadian living in a small Philippines fishing village where home construction is by home owners who build using rough chain saw lumber on soft wet ground. This video stressed thinking from the ground foundation upward leaving NO weak points anywhere.

in normal loft space, if you put those beams in you will have a head height issue. they will only work in high roof space loft

Could you tell me where to cut the joist for the hatch ?

Can you please do a video on ridge beam size calculation.

Great video. What are the structural implications of using OSB or structural ply to board out the loft? If the boarding has structural value then does that further limit the need for deep joists? Or is the idea to have the joists pass requirements and the boards are just a structural bonus? Hopefully that makes sense and is not too silly a question.

Excellent videos and really informative. Do you offer any service for loft conversion design? It would be great to see examples of lofts that can’t be converted and not just because of height restrictions.

This is brilliant thank you. The calc is good also. I can't find 50 x 175 timber, it's all either 45 x 175 or 47 x 175. Will this make a huge difference?

Nice spreadsheet but it's not letting me use 45mm thickness timber?

Great video, can you run the joists to load onto the floor binders also?

My 1960's semidetached bungalow loft is 10m from gable wall to gable wall, would the principles in this video still apply? Could I use 2x 5m joists meeting in the middle to span the new floor? Could you please cover something like this in a new video as I don't see much on bunglaows. Thanks

Robin , firstly thank you for the videos very useful and educational , Q: instead of using joist hangers , providing enough fixings where used could you use joists along the wall to support the floor joists ? thx again Rick

what CAD progrmme are you using?

Hi Robin I am looking to create a storage area in the roof space of a small (3.6m x 3.2m) ground floor bedroom extension at my daughters house. The exterior walls are 275mm cavity, 102 brick 75 cavity, 100 block. The roof is a cut rafter design and spans the 3.2m dimension. The roof pitch is 42 degrees and the length of the roof is 3.6m. There are two 150mm x 75mm wall bearing timber purlins, (at mid span of the rafters), and one 150mm x 75mm wall bearing timber beam at mid span of the ceiling joists. I would like to span the new storage floor joists in line with the rafters, sitting on top of the wall bearing ceiling beam and being supported at the ends via short hangers fixed to the wall bearing purlins. In effect creating a small "cradle" spanning 2m. I've downloaded your floor calculator (thank you very much for this) but don't think I can use it for the arrangement I've described. I realise the ceiling joist support beam and the two purlins will carry some load, but the storage area will only be a 2m wide strip along the 3.6m length of the roof, minus the loft hatch area. It will also only be about 1.1m high at the ridge and used for storage of very light items such as empty suitcases and Christmas decorations. Any help or advice on this small domestic project would be very much appreciated. Kind regards, Robert

great video, this is exactly what i want to do in my victorian loft however, i do have 1 question. Instead of attaching individual joist hangers into the brickwork you mentioned a wall plate! how would i attach a wall plate and secure it to really soft victorian brickwork? just screwing a piece of wood to these bricks would really worry me.

Hi Robin, Great informative video. What CAD / design software are you using? I am also curious if you use Formply plywood for the flooring? Many thanks, Ethan - Australia

Very good explanation and most of things coverd but most basic questions remains unanswered which is floor joists which will be probably 3 or 4 meters long will go in loft throuh tiny loft access??

Great videos… may I ask what software you are using for the illustrations?. Thanks Jas

What’s your thoughts on insulation below the new loft floor? I think we’re looking for average 280mm, a cross the surface, using 300 between the joists

As a joiner I would space the joists at 400mm centres, less cutting, less waste.

Hi Robin, looking to board out my loft and am using your calculator for the joists. My span from wall to wall is 3500mm with 500mm joist centres, if I use a 50mm thick by 175mm deep C16 grade joist the calculator says this will pass but I am not able to source this size of timber locally. I can source 47mm thick by 200mm wide C16 joists but the calculator does not allow me to input 47mm for the thickness. Do you think this size of joist will be suitable? Thanks Adam

Hi Robin could you do a video on how you would do this kind of work on a hipped roof with perlins

Change the joist centres to 400mm and the floorboard would work out without having to cut. The floorboards come in at 1200mm and work out perfectly with 400mm joist centres.

Why not use tongue and groove OSB? Readily available in France.

Great. I am considering loft conversion but the walls upstairs are studded and I have not long had the roof re-slated so probably a no go if I need to install flitch or steel beams.

Good informational video. Shame you cannot download the spreadsheet without signing up for some expensive download sites

Huge thanks for all the great videos. Silly question: If you do the work yourself as an amateur project what is the best way of finding a good BCO please?

Hi Robin Thanks for all the videos. My question is in relation to a typical London Victorian mid-terrace house (4.5m wide). If the whole building is empty and the ceilings are all being knocked out anyway, and you have the option of removing and adjusting all the ceiling joists, what options are there for a more efficient use of space and materials. For example, can new floor joists for the loft be placed on top of the existing front and back wall plates and in the middle placed on the spline wall, thus avoiding the need for steel beams for the loft floor? Separate to that, is it possible and worth lowering the hight a first floor rooms (from 2.6 currently to 2.4) to add a bit more room in the loft? Most loft conversions seem to be designed to, for example, not disturb the ceilings below, etc., but if none of those were an obstacle, rather the only limits were the outer shell of the building and, of course, building regulations, what could be done? I have some other thoughts/ideas I can add if you think the general question has value. Thanks

I made the scoreboard DIY error of doing exactly what you suggested, not doing in the video. My question is without removing the the roof tiles how would you get approval side lengths of timber through a standard size loft hatch.

Aren't the hangers timber to timber hangers you're using in the video

Discovered your videos recently and they are great but I'm always left wishing you'd cover a standard 1930s semi because the videos never quite fit my use case. Great work though.

What about a timber frame house?

Really good lesson...my roof runs long and i dont really have a wall to run the new beams to once off the gable end, the next wall is the other gable end about 30 metres away. Its a trussed roof design. What to do?

why not just put 2in rigid insulation on top of joist then 3/4 plywood?

Hi Robin, my loft has been converted by previous owners but they have just placed boards directly onto the ceiling joists. I want to fix this however there isn’t enough headroom to add a structure above as you have shown. Can it be done in parallel to the current joists bust just slightly higher? I was planing on supporting them by the Perlins since there seems to be secondary perlins low down near the ground. Does this sound reasonable?

What program is this?

I have a truss loft set up and I'm trying to board it out and raise the height because of the thick insulation but don't want to use crappy plastic stilts. Can I use this concept to fit floating joists on hangers then board?

what CAD software please?

Thanks for the calculator, VERY useful for me to try and work out how to take my attic conversion a step at a time

What is the computer program you are using for this please? Great video

I have a new build house, 2019, it’s detached and has a trussed roof, I would love to know if it would be possible to convert the loft. I have quite a span from gable to gable, maybe 10m/11m so I was wondering if it would be possible using normal method of gable to gable steel and a dwarf wall to act as purlins if that makes sense?

Hi Robin, would it be ok if you instead have the joists on brackets from end to end to avoid having to pocket out a load bearing wall.

When insulating can you use 100mm insulation inbetween 120mm joists?

How would you approach this if you don’t have an internal load bearing wall?

What software is that

I’d be interested to know a work around in a 50s detached bungalow (so no gable wall to fix hangers/joists). Could you span wall plate to wall plate parallel to existing ceiling joists, but keep separate from the ceiling joists, and pack slightly under the new joists to separate from the ceiling below?

I cant get such long wood up their what i do

Out of curiosity. I want to do the same in my bungalow, however, the distance from end to end is approx 10m. What would be the solution using your method as i will never get 10m lengths through the loft hatch 😂 Thanks in advance

Might be missing something but if the spacing for the loft booards needed to be 600mm why cant you drop it down to 300mm and use smaller timbers?