Really useful and interesting and something I will consider, thanks. I saw one comment that asks why builders don't usually do this. The main reasons are that old cut roof ceiling joists are usually bowed to hell and we usually jack the old ones up and fix them to the new larger joists, creating a flat(ish) ceiling. Also, inspectors can get very funny about you using the old timbers for structural purposes, as they're not sure of it's grading. You'd potenially have an arguement on yours hands and often just easier to use new. This tool might change that balance though 👍

So glad to have found this site. I felt there had to be such a work around. And now the homework begins. Cheers

💥Get your FREE timber joist span tables: geni.us/timbercalculation

Very interesting. In 26 years I've only ever seen this done once in a loft conversion and it was an architect that specified it. If I remember right, existing was a 6x2 and we added a 2x2 on top but building control said it has to be glued and screws have to be a specific distances. It's an incredibly cheap way to do it. Perhaps that tool is a bit too complicated asking for loads. Etc. All u need is my span is this, my existing joists are this so what is the minimum I need to add and what size screw an centres do I need.

Splendid video. Thank you. How about using glue as well as screws?

From a non structural point of view , you would want new floor joist and floor to be as independent as possible from the existing ceiling. Thats due to sound/noise/vibration propagation. To that end , if at all possible you'd want underside of new joists installed higher than and not connected to the existing ceiling joists. This would of course have cost implications but going about it this way, you are isolating to a degree of course the loft from the level below. Seen that done on several projects. Architects did their job properly. Builders on the other hand were less than impressed due to the additional work/hassle 😀

Interesting, looks like a virtual suspension bridge

Why are the screws at an angle like that? Is there any benefit rather than screwing them perpendicular to the grain?

Brilliant thank you. I'm looking at boarding up loft. 1930s property with trusses. How do I calculate moving the trusses to make space for the room please. Keep up the good work I love your videos

Interesting video, many thanks Robin. Could you do one sometime on screws Vs nails. Normal screws are not as strong as nails in shear. So for roof framing nails are normally used and carefully positioned so any slight splitting will not be significant. So my questions for this joist reinforcement - are these special material screws (too small for coach screws), and is the angle calculated to put the screw in tension rather than shear? Presumably as you move from the Centreline the screw angle from vertical should increase in the ideal case? (Ok too complicated so 45 compromise chosen). For those of us with roof trusses, but bracing faults, could this Fischer tech be used somehow to correct the length of braces (longitudinal and diagonal). Again I get back to screw angles and screw materials and the best way to fix new timber to an old one. Traditionally though is faulty bracing just removed and redone? (tricky to get large timbers into the loft without removing tiles). The other question is roof truss timbers should not be drilled (any dia?) to avoid weakening. What consideration should be given then in fixing to old timbers (that gives me a preference for screws then if they are suitably thin). Enough material for another video? Also do we need to take bracing faults more seriously now gales getting more frequent? Many thanks again.

Hi. What are the screws out in that way? How is this meant to strengthen the old joists? If they are meant to be on top of the old ones are the timber ones meant to be the same length? Thanks

Hi Robin, thanks for this very useful video. Is the dead load of 0.4 kN/m and variable load of 0.7 kN/m representing loft storage purposes? Thanks for your help.

Ive boarded my loft using loftzone 150mm support and galvanised steel cross beams which run perpendicular to the joists. I want to put some 'dwarf' stud walls up on either side so that i can put away things for storage and hide away the insulation at the edges of the roof. Im woindering if i should bolster the joists but wonder if what ive done is giving some strength.

I have 3" x 2" joists in my loft space, they are too weak to risk standing on, this might be the solution I am looking for, the only problem I would have would be getting the new joists up into the loft, as they would be too long to get in through the hatch :( . Good video, thanks.

Thanks Robin I wanted to strengthen my existing joists in the loft for storage. Does this still work if there are ceiling binders at 1/3 span of each joist? What would be the correct strategy in that case? If one were to sister only between the ceiling binders, there would be an unsistered region going under each ceiling binder, but the unsistered span would be so short 44mm or something that would this matter?

Hi Robin, Thanks for the video as usual. I was wondering if you have done videos about the masonry checks and which one are the best ways of working them out. (Adding a few courses or 7Nblock or engineering brick). Also, I wanted to know your thoughts about supporting a 10m beam with a reaction of 100KN (ULS) over brickwork. Thanks!

I noticed you left the width of beam at 100mm, not many joists in the loft are 100mm, mine are 3x2 but when adding 95mm x 45 or 72mm x 45mm to existing joists it fails even lowering variable load to 0.25. I have an unfavourable house when it comes to supporting walls so looking at alternative ways to add a room and I thought this may work

What about thermal bridging when the floor boards are put on top.

So is this straight on top of the existing joists? I have always done the new wood structure 90 degrees to the original design. Which is the better way?

Hi there my loft joust are 2”x3” and wanted just floorboards fir stuff like Xmas tree , anything I dnt want to have on rooms , I am worried if I put new joist and floorboard , the existing joist won’t take the weight , what should I do ? Or no need to be worried and it’s ok ?

Hi There, today i had a company come and assess to quote for boarding my loft. They said they can not use their Loft Zone system, which is to put plastic props on the joist and run boards above insulation height; they can not use this system as my joists are about an half inch less than specified regs! IS there another cheap (ish) and efficient way for me to board my loft above insulation?

Hi Robin, Once you download the software is it always free to use? Thanks

Hi Robin, Many thanks really useful information - unfortunately I cannot find the Woodfix software on the Fischer Site is there an upto date link you could share please - Geoff

Why do most builders when they are converting the loft floor not do this? They tend built a completely separate floor with steel beams.

i would love your advice on my Crog Loft 1790s, floor joists redone 1970. But i feel any calculation would be a guesstimate due to notches cut out for plumbing and my use of flitch plates. Mixing new soft pine with the old pitch pine would also need assuming the weakest of timbers.

Or just pva them on

@aprilwilkerson I love watching your videos and I think it’s funny that your add spot featured a facial tool, I also have a tool I have often wished to give you a facial with. HMU. Don’t worry I won’t get it in your hair😇