Joist hangers - what am I missing

[joe90]

Ah, misunderstood, yes as @PeterW says, standard stuff fir “normal” builders (as apposed to us “self builders”).

[Moonshine]

O.k i think that i am going to go away from a ledger board, and use a metal inbuilt hanger as the brickie i have talked indicates that he can work the coursing to my split level house.

 

https://www.strongtie.co.uk/products/detail/joist-hanger-for-masonry/356#tab-technical-data

[Rishard]

In relation to this topic. I’ve installed ledger boards in the past with resin bolts and had good success. 
 

I haven’t ever wet plastered behind the ledger boards. Would you just wet plastered the area behind the board before installing it or the whole room? Obviously difficult if there is no floor in yet. 
 

I plan on using ledgers with my design and eco joists on 400mm centres. 
 

I remember once spacing the ledger off by 25mm behind the each resin bolts and had so the electrician had an easy route down for his cables. Do we think this is advisable or should be avoided? I have a concrete ground floor so imagine most of the socket ring main and lighting coming down from the first floor void. 

[Iceverge]

8 minutes ago, Rishard said:

I remember once spacing the ledger off by 25mm behind the each resin bolts and had so the electrician had an easy route down for his cables. Do we think this is advisable or should be avoided?

 

Excellent plan for your sparky but I'd worry about the cantilever effect of having the ledger off the wall. Some calcs might be prudent I think. 

 

You could always pre chase the routes for cables behind the ledger and drill an angled hole through the ledger to take the cables. 

 

11 minutes ago, Rishard said:

I haven’t ever wet plastered behind the ledger boards. Would you just wet plastered the area behind the board before installing it or the whole room?

 

The area just behind the ledger should be fine. You could always carefully not bother and just slop some airtight paint above and below it afterwards. 

[Rishard]

9 hours ago, Iceverge said:

 

Excellent plan for your sparky but I'd worry about the cantilever effect of having the ledger off the wall. Some calcs might be prudent I think. 

 

You could always pre chase the routes for cables behind the ledger and drill an angled hole through the ledger to take the cables. 

 

 

The area just behind the ledger should be fine. You could always carefully not bother and just slop some airtight paint above and below it afterwards. 

 I hear what you mean regarding the cantilever. I will have a word with the sparky and see if a pre planned conduit run or chase could work behind the ledger. 
 

In regards to airtight paint. Do you mean seal the top and bottom edge of the ledger to the blockwork? Would an airtight silicone type mastic be good for this if the timber shrinks? Never used airtight paint direct to blockwork/timber. Am I right in thinking you’re talking about applying it at this junction, prior to plastering? 

[Iceverge]

4 hours ago, Rishard said:

Do you mean seal the top and bottom edge of the ledger to the blockwork? Would an airtight silicone type mastic be good for this if the timber shrinks? Never used airtight paint direct to blockwork/timber. Am I right in thinking you’re talking about applying it at this junction, prior to plastering

 

Yup, airtight paint would give you the option of bringing the airtight layer up and well clear of the floor construction to meet the wet plaster later on. 

 

Airtight sealant would work but you might find it tricky to plaster right to the line of the sealant. 

 

Dilute the airtight paint 5:1 with water as a primer before applying the top layer . 

 

You could always use airtight paint entirely behind the ledger before you attached it to the wall. 

 

Don't forget to put some mastic or sealant in the holes the bolts go into the wall too and to airtight paint the chase behind the ledger. 

 

 

 

 

Edited March 22, 2025 by Iceverge

[Rishard]

That all sounds pretty sensible and practical. A much easier approach then trying to get the plaster in to skim a meter strip around the whole joist band area. 
 

Will look into airtightness paints next. 
 

My eco joist supplier is able to provide my joists with an amount of ‘trimmable’ ends in order to get the best fit. 

 

In reality it is much more difficult building up all the masonry 2 storeys without the first floor to work off. We’re about done now so looking forward to putting a roof on and installing a floor. 
 

[Iceverge]

13 hours ago, Rishard said:

reality it is much more difficult building up all the masonry 2 storeys without the first floor to work off

 

No need to do this is have thought. 

 

Just build the walls say 1-2 courses above the first floor height, partially chase them for your services. Paint on airtight paint , fix ledger, fit first floor. Carry on as normal. 

 

Thinking about it, drilling concrete, cleaning the hols and inserting resin fixings is a ball ache. 

 

Would it be easier to build in m10x180mm bolts to a mortar bed with 50mm washers in the cavity side. And leave 80mm protruding inside 

 

Drill 20mm holes in the ledger for some shuffle room and bolt in place. 

[Indy]

Holy thread bump......

 

Coming to this thread as we’re in a similar situation. 2 storey (plus loft) house being built in masonry (Celotex 7.3kN high strength blocks) which will be rendered on the outside and wet plaster on the inside. Floor will be Posi-joists which I always assumed would be done using joist hangers. Spoke to one of the brickies/foremen on site who mentioned that they would be using resin anchors rather than joist hangers as it’s easier to level up using a laser level – compared to joist hangers.

 

Not sure I fully understood it when he mentioned and spent the weekend reading up about it on ChatGPT and Gemini. The unanimous verdict was not to use the resin anchors into the Aircrete blocks as the fixings were going to come loose in the long term and masonry supported joist hangers are the way to go. Spoke to the builder / boss man who confirmed he was going to use joist hangers. Feels like a win but I’m not sure reading some of these comments. We are aiming for an airtight house with parge coat/wet plaster inside and silicone render outside. Is there a preferred way to go? I don’t want squeaks/mechanical fixings failing on me in the next 10-15 years.

[Iceverge]

Bin the aircrete and the PIR. 

 

Dense blocks and mineral wool batts in the cavity will out perform it in reality. 

 

 

 

[Oz07]

Why hangers instead of building into the wall?

[Indy]

15 hours ago, Iceverge said:

Bin the aircrete and the PIR. 

 

Dense blocks and mineral wool batts in the cavity will out perform it in reality. 

 

 

 

Too late for that - the ground floor blockwork is already in using the aircrete blocks and PIR. No plans to change it now as the materials for the first floor have also been ordered already. 

[Indy]

14 hours ago, Oz07 said:

Why hangers instead of building into the wall?

Can you enlighten a simple mind like mine how that would work - trying to learn all the different variants of putting joists up!

[Iceverge]

15 hours ago, Oz07 said:

Why hangers instead of building into the wall?

 

Airtightness. 

 

 

[Mr Punter]

I have done similar using resin anchors to face fix a timber ledger to the wall, then timber to timber joist hangers for the joists.  It means you have more freedom in floor height and better airtightness.  Your blocks should be fine for this as the ledger will have fixings every 400mm.  Cleaning the drilled holes with brush and blower is key to a very strong fixing.

[Nickfromwales]

1 hour ago, Mr Punter said:

I have done similar using resin anchors to face fix a timber ledger to the wall, then timber to timber joist hangers for the joists.  It means you have more freedom in floor height and better airtightness.  Your blocks should be fine for this as the ledger will have fixings every 400mm.  Cleaning the drilled holes with brush and blower is key to a very strong fixing.

Do the fixings in vertical pairs, 75mm down from the top of the ledger, and 75mm up from the bottom, and repeat until you have run out of money to buy more resin and bar. You'll only get one chance to do this right, so invest in the important things.

 

100% defo blow the holes out as above, but this will be your builders job and you'll need to impress upon them the job is wanting doing properly where he may say "don't teach me to suck eggs", even if under his breath of in his head..... If they're not on day rates, offer to pick up the tab for the extra hours adding more fixings, which should keep them happy.

 

Joist hanging off legers is the way forward here for sure, as long as the fixings are at higher frequency AND robust.

[Indy]

Well this is all quite conflicting advice with what ChatGPT, Gemini and the vast majority of the internet sources advise. All the online searching I did discouraged me away from the ledger board approach and said the hangers must be built into the masonry for longevity. The ledger board is only held up using chemical bonds and that the weight of the floor above it would eventually work those bolts loose - especially as I'm using Celcon blocks (which can't be changed).

 

So I spoke to the builder who has confirmed that he'll be using joist hangers built into the masonry. Much ado about nothing in the end - though I did get to learn something new I guess. 

[Oz07]

9 hours ago, Iceverge said:

 

Airtightness. 

 

 

Tony tray no good?

[Nickfromwales]

2 hours ago, Indy said:

Well this is all quite conflicting advice with what ChatGPT, Gemini and the vast majority of the internet sources advise. All the online searching I did discouraged me away from the ledger board approach and said the hangers must be built into the masonry for longevity. The ledger board is only held up using chemical bonds and that the weight of the floor above it would eventually work those bolts loose - especially as I'm using Celcon blocks (which can't be changed).

 

So I spoke to the builder who has confirmed that he'll be using joist hangers built into the masonry. Much ado about nothing in the end - though I did get to learn something new I guess. 

The hangers are just fixed into the Celcon blocks, so out of the fire, and into the frying pan. Just ask your builder to ping string lines for the hangers to be dead straight and level, as that is often 'nearly good', but could have been better.  

 

2 hours ago, Indy said:

The ledger board is only held up using chemical bonds

....."only"..... which are strong as feck.

 

Ledgers are held up by bolts, not by the resin.

 

Bolts for the sheer strength, and clamping force, and the resin anchor for holding the bolts (M16 bars) in place.

 

I'd happily argue that multiples of small fixings using expansion for their means of purchase would degrade the material that the block was made out of, as these are many, and very close together.

 

@Gus Potter @saveasteading?

[saveasteading]

You called?

 

3 hours ago, Nickfromwales said:

multiples of small fixings

I have only skim read. But I don't see a mention of multiple small fixings... that would apply to a lightweight hanger nailed to  a wall plate though.

This happens to be my preference I think. A timber the same depth or greater than the joist will bolt to the wall without stressing it to much. The deeper it is, the more robust it will all be, and easy.

As above you must watch the builder very closely.

Dont drill too big a hole... the bolt should just fit without force. Threaded rods are usually thinner than stated.

Grind the hole, don't sds it.

Brush out all dust.

Look at the resin mixing and discard it until it is uniform colour.

Turn the bolt as if slowly screwing into the hole this gets the resin fully into the thread. And continue til resin is screwed out of the surface. This also picks up remaining dust.

Don't touch it until it is hard.

Use washer and tighten the nut until the wood just distorts.

 

Then you use 80p hangers and lots of nails.

 

OR use heavy duty hangers fixed into the mortar coursing.