How best to raise boarded out area in loft to increase insulation levels

[marshian]

Well I’ve sat and thought about it for a few days and the price of I-Joists seemed to only make it viable for the centre section (so I’d end up removing quite a lot of boards) 

 

then I came across an advert for some 2840 mm by 240mm I-joists thar were surplus to requirements so I’ve bought 25 of them for £237 which seemed like a bit of a bargain

 

I can do pretty much most of the loft area that is already boarded and maybe a couple of crawl walkways to enable me to get into the two smaller loft areas for access to wiring/poe cabling for cctv cameras which is pretty much in every corner of the house (downside of being burgled is a tendency to go way over the top with security cameras)

[joe90]

Sorry didn’t get back to you, I will in the morning when I get home (honest) 🙄But I just noticed you have a solution .

Edited September 21 by joe90

[marshian]

50 minutes ago, joe90 said:

Sorry didn’t get back to you, I will in the morning when I get home (honest) 🙄But I just noticed you have a solution .

oh no problem @joe90 we all are busy with life

 

I’m still a smidge concerned about the weight even with I-Joists (which are 1/3 of the weight of timber equivalents) but I’ve been up in the loft today and noticed part of the loft already boarded is actually double boarded - I obviously didn’t trust what was already there and boarded over the top!!!!!)

I reckon some of the boards I won’t be able to use so I’ll not go right to the edges 

 

My delivery of ventilation gap things arrived today to stop the loft insulation going into the eaves and stopping air circulation - should also stop air washing thro the insulation too….

 

Like most moulded components I’ve seen better quality but for £1.96 each and I needed 32 it’ll stop me worrying about ventilation issues.

 

only thing I will need to buy is the loft insulation rolls so currently investigating options and pricing for that.

 

just need the weather to turn a little - currently it’s 30 deg in the loft (south facing roof with concrete tiles that do seem to absorb a lot of the sunlight and cook up the loft)

 

 

[marshian]

Collected the I-Joists tonight - they've been dry stored for a while it seems but are new and never used

 

Need to have a google and see how best to join them end to end 

 

1. minimise cutting losses

2. provide addition strength where the join isn't above a roof truss

 

I was thinking OSB sandwich plates either side of a join and either screw thro or bolts??

 

Before anyone goes a bit nuts bear in mind they are being joined over a max span of 600mm - it's not like they are being joined to create a larger span - that would be a bit daft

Edited September 25 by marshian

[Gus Potter]

On 10/09/2024 at 20:30, marshian said:

Bit of background

Hiya.

 

There is a lot of well meaning advice here in the posts above. I do this as a day job and you are inviting trouble. I see this all this time and folk end up in a nightmare! There are maybe one or two SE's on BH who know about this stuff.. the rest are.. it's not their day job.

 

I can't see all of the roof truss layout but I'll hazard a guess that some of your intermediate walls are non load bearing. Now it looks like you have ground floor extension with a beam over.. if you change the loading pattern you could over load that beam for example that allows access to the extended part. You are playing with fire here.

 

Just say you come to sell the house and a surveyour sees you have made alterations  to the attic. You won't be able to sell the house... even if you think your alterations are sound. You'll need an SE to sign it off.

 

Please do this right and pay an SE for advice.

On 10/09/2024 at 21:26, elite said:

Loftzone do a product that looks more stable than the cheap legs:

Aye but this is let's say putting a bit of a gloss on things more often than not! If loft zone want to get in touch with me them I'm all ears! I would love it if they have a good economic load bearing and compliant solution as I could sell this day in and day out and sign off on it too!

 

I keep pulling these folk up about the shite they are selling for say fink truss aplications. Some of them approach me to sign off their designs.

 

OP and there are a few of these loft boarding  folk proposing insultating with spray foam insulation so we need to have a look at the dew points so your roof does not end up rotting away!

 

Now your basic distributed design load on a modern lightweight roof truss is 25 kg/ square metre applied to the ceiling chord. There are other loads but for now. Add 11 kg/ m^2  for your flooring leaves you with 25 -11 = 14 kg tops depending on the truss spacing.. Most of then are selling on the basis of 25kg.! Now take the insulation wieght off this. Then go back to the truss manufacture and ask.. can we insulate out our loft and floor a bit of it.. if so how much load can we put on the new floored bit!

 

Now some of these loft folk are saying.. we can give you a bigger hatch.. now you are cutting a structural truss. Just look at the sizes of the bit of wood! Even as a lay person you must be able to see they are slim and slender.

 

Now just say you are going on holiday to Spain and the window in the airplane is a bit small. I pitch up and say.. no problem pal.. I've brought my Dewalt and I'll just cut this tiny wee rib out as it is so small it can't be doing much, fit a new window bigger from B & Q and you be good to go!

 

 

 

[marshian]

9 hours ago, Gus Potter said:

Good stuff <snipped>

 

Now just say you are going on holiday to Spain and the window in the airplane is a bit small. I pitch up and say.. no problem pal.. I've brought my Dewalt and I'll just cut this tiny wee rib out as it is so small it can't be doing much, fit a new window bigger from B & Q and you be good to go!

 

You were doing so well until the last section ^

[joe90]

Question @Gus Potter, what percentage of over engineering is applied to building structural calculations.?

 

I did a job for a customer and the BC officer insisted on a huge timber support (which I and the customer thought was OTT). The customer was a plane designer and he told me they worked on 5% over what would break 🤯.