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, 2024 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, 2024 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 🤯.

[marshian]

the passing of @joe90 reminded me I hadn't come back to this topic

 

So taking on board the sensible part of @Gus Potter's post and finding no local SE remotely interested in doing any calcs - the majority didn't even respond to an email and those that did said it wasn't worth their while or advised me it would be prohibitively expensive - I guess expensive is a relative thing the few that did respond wouldn't even give me a ball park so I'll take that as a brush off.

 

So in the interests of getting my head round it I did some myself - unfortunately I do them the practical way

 

A section of the loft I stripped of the existing boarding that has been down for 30 years

 

I was surprised at the weight of the boards removed - it was all double boarded with 10mm OSB and 12mm chipboard (pretty sure I laid the OSB and then found it a bit flexible underfoot so double boarded it with 12mm Chipboard to stiffen it up

 

So area covered was 13.8 m2

 

Weight of the boarding removed 197 kgs

 

So loading was 14.2 kgs per m2 for the old boarding

 

So new boards 18mm OSB work out at 10.3 kg / m2 so 142 kgs

 

To raise the floor area in this section I need to use 7 I-Beams and at 3 kg per m length that's 50kgs

 

Total weight 192kgs for new raised loft flooring (or 13.91 kg/m2)

 

Oh but I hear you say what about the insulation - so lets cover that

 

150mm superglass loft insulation is 10.76 kgs per pack - each pack covers an area of 7.71 m2

 

That's 1.38 kg /m2

 

100mm superglass loft insulation is 11.28 kgs per pack - each pack covers an area of 12.12 m2

 

That's 0.9 kg /m2

 

So based on doubling up 150 with 100 a 13.8 m2 area will need 32 kgs of loft insulation or 2.28 kg/m2

 

So the total load, I-joists, boarding and loft insulation is 16.2 kg/m2

 

I'm quite comfortable with that.........

[marshian]

So first section completed

 

 

Yes I know the edge closest to the roof tiles and felt isn't supported - it's just acting as a dust/condensation cover for the insulation

[Gus Potter]

22 hours ago, marshian said:

So taking on board the sensible part of @Gus Potter's post

 

For all I've attached a handy design guide (old but still provides inspiration) to trussed rafters. Page three has all the shapes of common types that can help at the concept design stage. It's well worth a look at as it will familiarise you with the terms that say MBC, Pasquills etc use. It is a mine of information with good diagrams.

 

@marshian.. So glad you have taken note of my dramatic laymans guide and found some inspiration. From time to time I use a bit of drama and real life examples as Engineering etc should be fun!

 

22 hours ago, marshian said:

So the total load, I-joists, boarding and loft insulation is 16.2 kg/m2

On the face of and taking your calcs at face value this leaves about 25kg (the BS design load) less your 16.2 kg = 8.8 kg distributed load per square meter. That includes you standing and moving about. Do you treat that as a point load or not.. I'll leave it up to you to decided for now.

 

Just because you had a certain amount of load on the trusses before does not mean you can use this as a benchmark. You have to understand what the original design loads were. You also have to know about the different design codes. Are you working to the Eurocodes or the BS. In your case your trusses are probably designed to the BS code.

 

22 hours ago, marshian said:

I'm quite comfortable with that

Ok but if something goes wrong then it is your neck on the line don't forget.

 

As before I've attached an old design guide from Wolf Systems that has the BS truss loadings on page 4. Have a read of this for your own piece of mind. You may want to review you calcs.. if you need to make changes then don't be embarrassed about it.. this is part of the normal design review process.

 

 

 

 

 

 

 

 

 

 

 

 

 

Trussed-Rafter-Tech-Manual Wolf.pdf

Edited February 4 by Gus Potter

[marshian]

1 hour ago, Gus Potter said:

 

For all I've attached a handy design guide (old but still provides inspiration) to trussed rafters. Page three has all the shapes of common types that can help at the concept design stage. It's well worth a look at as it will familiarise you with the terms that say MBC, Pasquills etc use. It is a mine of information with good diagrams.

 

 

Diagrams are handy - I'm pretty sure I have FInk style Trusses

 

1 hour ago, Gus Potter said:

So glad you have taken note of my dramatic laymans guide and found some inspiration. From time to time I use a bit of drama and real life examples as Engineering etc should be fun!

 

I took note - just had other things going on

 

As far as drama and real life examples go - be careful using examples like cutting holes in aeroplane windows with a multitool - you might think it's humor/fun but it may not be received in the same way - that's the problem with text on the internet - you don't get to see the facial expression as the humor/fun is delivered

 

1 hour ago, Gus Potter said:

On the face of and taking your calcs at face value this leaves about 25kg (the BS design load) less your 16.2 kg = 8.8 kg distributed load per square meter. That includes you standing and moving about. Do you treat that as a point load or not.. I'll leave it up to you to decided for now.

 

the storage up there is pretty minimal (xmas decorations, empty suitcases, my stock of foam pipe insulation and the odd tote bin of things I don't want to throw away) and items are well spread out

 

I'm not using it as another room but I do want to be able to get access to all areas of the loft easily - I'm not happy with 400 mm of loft insulation over the top of trusses so I don't have a clue where I can stand safely without putting a foot thro the ceiling below (that's why it was boarded originally)

 

1 hour ago, Gus Potter said:

 

Just because you had a certain amount of load on the trusses before does not mean you can use this as a benchmark. You have to understand what the original design loads were. You also have to know about the different design codes. Are you working to the Eurocodes or the BS. In your case your trusses are probably designed to the BS code.

 

You raise a valid point but 30 years my loft has been boarded out and I've seen no evidence that it was in any way excessive loading - no sags or cracks in the ceilings

 

They (trusses) are actualy marked up with manufacturer (swedish I think) and a BS std - I think from memory BS 5268 because the cold water storage tank is in the loft framed off the trusses - I need to check and note down the details

 

One thing I would say they aren't the spiders web of skinny timber I looked at in a friends new build house - they looked like match sticks holding the roof up!!!

 

1 hour ago, Gus Potter said:

Ok but if something goes wrong then it is your neck on the line don't forget.

 

As before I've attached an old design guide from Wolf Systems that has the BS truss loadings on page 4. Have a read of this for your own piece of mind. You may want to review you calcs.. if you need to make changes then don't be embarrassed about it.. this is part of the normal design review process

 

Appreciate that it's my neck on the line and I do have a habit of "over engineering" stuff so the advice is appreciated

[Gus Potter]

52 minutes ago, marshian said:

As far as drama and real life examples go - be careful using examples like cutting holes in aeroplane windows with a multitool - you might think it's humor/fun but it may not be received in the same way - that's the problem with text on the internet - you don't get to see the facial expression as the humor/fun is delivered

Fair comment and accepted. For the avoidance of doubt my core qualification is my Masters Degree in Civil Engineering.  I specialise in Structural Engineering but have now wondered ( it's a natural progression for me) into the Architectural design side. The key here is the word "Civil". My underlying responsibility lies to the public first and foremost.. not the Client who may be paying my fee.  Now like many other Civil Engineers @saveasteadingwho may say design a dam we have to carry a burden of responsibility. If we get it wrong we can kill lots of folk. This moral, not least, responsibility comes with the job.

 

To be frank sometimes the job keeps me awake at night! Have I got it right, have I done something daft that could fall down and kill folk? The job I do is massivley creative and rewarding but there is a price to pay for the privalge.

 

I think engineering should be fun.. it becomes particularly rewarding when you have the skills to design from first principles.. which my education has taught me to do. What makes it even more fun is when you sit down with a self builder and value engineer their build / get initial prices from builders and get involved in the finance side of things. For me I then get to see all of the picture and feel part of the design team.

 

But yes the internet is faceless and sometimes humour does not transfer. I'm a bit deaf and lip read a bit so know all about that!

 

 

52 minutes ago, marshian said:

I'm not using it as another room but I do want to be able to get access to all areas of the loft easily

Fair enough. Your approach is pragmatic in that you know you need to manage the loadings. Hope the Wolf Design guide gives you some food for thought. Be careful if you want to muck with the roof bracing.. you may be tempted to alter this?

 

 

 

 

 

Edited February 5 by Gus Potter

[marshian]

9 hours ago, Gus Potter said:

Fair comment and accepted. For the avoidance of doubt my core qualification is my Masters Degree in Civil Engineering.  I specialise in Structural Engineering but have now wondered ( it's a natural progression for me) into the Architectural design side. The key here is the word "Civil". My underlying responsibility lies to the public first and foremost.. not the Client who may be paying my fee.  Now like many other Civil Engineers @saveasteadingwho may say design a dam we have to carry a burden of responsibility. If we get it wrong we can kill lots of folk. This moral, not least, responsibility comes with the job.

 

To be frank sometimes the job keeps me awake at night! Have I got it right, have I done something daft that could fall down and kill folk? The job I do is massivley creative and rewarding but there is a price to pay for the privalge.

 

I can understand why that would keep you awake at night but as you say if the job is creative and rewarding I hope the number of sleepless nights are minimal

 

9 hours ago, Gus Potter said:

I think engineering should be fun.. it becomes particularly rewarding when you have the skills to design from first principles.. which my education has taught me to do. What makes it even more fun is when you sit down with a self builder and value engineer their build / get initial prices from builders and get involved in the finance side of things. For me I then get to see all of the picture and feel part of the design team.

 

I'm with you on the fun bit - I work in manufacturing in a slightly weird role (started in manufacturing management - moved sideways into logistics and then sideways again into finance before my most recent role as a the sole business analyst but linked closely to operations

 

As a result I deal with everything from automation optimisation, scheduling, costing (lab, RM and OH recovery) as well as capital projects -  That might get me a a label of "A jack of all trades" and probably the back ground I have mean the std "master of none" doesn't actually apply 😉 

 

9 hours ago, Gus Potter said:

But yes the internet is faceless and sometimes humour does not transfer. I'm a bit deaf and lip read a bit so know all about that!

 

For me it's a consequence of text or rather the English language being easily miss interpreted - emails can be even worse!!! I do try to see any comment as "meant in a good and constructive way" I find that helps avoid issues or poorly worded responses that result in tensions

 

9 hours ago, Gus Potter said:

Fair enough. Your approach is pragmatic in that you know you need to manage the loadings. Hope the Wolf Design guide gives you some food for thought. Be careful if you want to muck with the roof bracing.. you may be tempted to alter this?

 

The Design guide was very useful and yes gave me food for thought

 

The roof bracing is exactly as it was built - where boards intersect with the bracing - the boards get cut to suit 🙂 

 

Anyway - I'm pleased to say last night I completed phase one - 1/3 of the accessible area is fully insulated and boarded - I can already see the difference in the ceiling temps of the rooms below (with an IR thermometer - only 2/3rds of the rooms below are covered by the improved insulation right now)

[marshian]

On 05/02/2025 at 00:29, marshian said:

They (trusses) are actualy marked up with manufacturer (swedish I think) and a BS std - I think from memory BS 5268 because the cold water storage tank is in the loft framed off the trusses - I need to check and note down the details

Took pictures so I don’t forget

 

 

 

 

BS 4978 - is what they are marked up as

[marshian]

Ahh google informs me that is the std for graded timber used in the trusses.

 

I'm pretty sure the Trusses would have been fabricated by local roofing company but they've been amalgamated into another company.

[marshian]

Phase I completed

 

 

So area covered = 1.5 m x 6.1 m - Yes I know it doesn't show insulation or boarding but it's all done

 

Now I'm on to Phase II (opposite side of the loft)

 

 

Boards are temporary just so I could lie down and roll out the insulation between the I-Beams

 

Next section requires me to lift the additional insulation I laid over the top of the layer between the trusses which will be a pain as it's all odds and sods

[marshian]

Still ticking along with this although the recent warm spell has made it a bit uncomfortable up there (it's currently nearly 5pm and my loft temp and humidity sensor is telling me it's 34.6 deg C and 32.5 %RH

 

One end from hatch to the gable wall is now fully finished

 

 

Other end with the water tanks in the distance I need to join the side section to the middle area

 

 

Also need to

 

1. Raise the lights up a smidge I keep clipping the with my head

2. Box in the shower extract fan

3. Insulate the loft hatch board and create a second trap door to increase the sealing

4. Re-do the pipework on Right that goes from Airing cupboard to the Cold Water store and F&E tank

[marshian]

I’d started a couple of tasks yesterday but not completed

 

finished 2 & 3 this afternoon

 

Boxed in the bathroom extractor fan unit (and insulated around the pipework inside the box) 

 

 

Lid is removable for maintenance or replacement but main purpose of boxing in was to use up some offcuts and insulate plus stop me tripping over the pipe

 

Loft hatch completed

 

 

This is the top hatch 25mm of celotex glued to a thin ply board

 

original loft hatch also lined with celotex 25mm to help seal up and also improve insulation properties of a badly fitting plywood hatch

 

 

It’s very noticable the impact on the PIV output, before with just the single plywood loft hatch when it was shut and the PIV was on you could feel the airflow escaping through the hatch into the loft 

 

now with the new set up you can’t so the PIV will hopefully reach places it didn’t before

 

Damn it was hot up there when I started!!!! Hatch open and patio door open I’m getting a decent airflow to push out the hot air and it’s down to a much more comfortable 28 deg C

[marshian]

Finished all the boarded area now

 

Also core drilled a hole in two of the four gable ends from the inside out and didn't explode the faces (Thanks @Nickfromwales - took your approach of slow and let the cutter do the work

 

 

Then slotted in a short length of soil pipe and capped it with a stainless steel vent plate

 

 

Heights don't normally worry me but this was working at the max extension of my ladder

 

 

Did the same on the other side of the house so I'm now getting a nice thro flow when the wind is in the right direction with an added bonus that loft temps are an average of 5 Deg C lower than they were before for same OAT

 

Humidity levels in the loft have reduced too

 

[Nickfromwales]

4 hours ago, marshian said:

Finished all the boarded area now

 

Also core drilled a hole in two of the four gable ends from the inside out and didn't explode the faces (Thanks @Nickfromwales - took your approach of slow and let the cutter do the work

 

 

Then slotted in a short length of soil pipe and capped it with a stainless steel vent plate

 

 

Heights don't normally worry me but this was working at the max extension of my ladder

 

 

Did the same on the other side of the house so I'm now getting a nice thro flow when the wind is in the right direction with an added bonus that loft temps are an average of 5 Deg C lower than they were before for same OAT

 

Humidity levels in the loft have reduced too

 

The apprentice has become the master....... 👌🙏