Just not happy about the concept of joist hangers.

[epsilonGreedy]

I get that masonry wall floor joist hangers are favoured over traditional in-wall fixing of joists in the pursuit of airtight homes but can these hangers cope with 100 years of cyclical loading?

 

Here is my beef. Driving a metal nail into a brittle masonry block to attach a hanger feels like an abuse of such dissimilar materials with long-term failure designed into the fixing. Next add 100 years of 80kg cyclical loading as humans walk around inside the home, stir in some thermal expansion and contraction loads on the hanger attachments and surely after a decade or two the hanger nails will start wobbling in the blocks? Then finally for a laugh apply that process to light thermal blocks.

 

Are my concerns unfounded?

 

The no nonsense commercial builder of a plot nearby has fitted his metal web floor joists direct into the inner blockwork and these blocks are heavy structural blocks I think. 

[MikeSharp01]

Has not seen this problem as I thought the joist hangers would be fixed to timber wall plates which are themselves fixed to the block work with chemical anchors or some such. Nailing direct into blocks sounds like the recipe for future problems exactly as you describe.

[ADLIan]

There are 2 basic types of joist hanger - onto masonry and onto a timber ledger. The masonry ones are built into the mortar beds and hook over the block - they are not nailed. The others are nailed onto the timber ledger. In both instances manufacturers give very strict fixing instructions.

[epsilonGreedy]

50 minutes ago, ADLIan said:

There are 2 basic types of joist hanger - onto masonry and onto a timber ledger. The masonry ones are built into the mortar beds and hook over the block - they are not nailed. The others are nailed onto the timber ledger. In both instances manufacturers give very strict fixing instructions.

 

 

Ok this is reassuring. I thought the lower part of the masonry hanger had to be nailed to prevent the lower half of the joist from twisting and thus promoting floor flex. There was a long thread here at the start of the year and some excellent photo detective work from forumites identified lack of nailing and thus twisting, having re-read those posts I now think the problem  related to wood to wood fixing around a chimney breast.

 

There is however another aspect mentioned in the Posijoist manual, they say if joists are expected to contribute to lateral wall bracing special hangers are required. I wonder if these require nailing.

Quote

Posi-Joists™ can be supported in masonry hangers at an external masonry wall. This method of construction meets the thermal and air leakage requirements of Building Regulations.  This detail does not provide lateral restraint to the wall unless a restraint type hanger is used, if standard masonry hangers are used restraint straps will be required. 

 

 

I am spending two days at the NEC exhibition this week and hope to get more technical insight from metal web joist manufacturers.

[Mr Punter]

http://www.strongtie.co.uk/products/detail/safety-fast-hanger-for-i-joist/402

 

These go over the blockwork, so give lateral restraint.

[Luckylad]

2 hours ago, epsilonGreedy said:

Then finally for a laugh apply that process to light thermal blocks.

Hi

I wouldn't use thermalite or celcon blocks again. They've hairline cracked all over my internal cavity block. I'm now putting silicone over the cracks before I parge coat and dot n dab.

I used fibolite on the outside skin,I haven't found 1 crack in them yet.

It's extremely difficult to get a fixing in light thermal blocks as well 

[Temp]

 

1 hour ago, epsilonGreedy said:

I thought the lower part of the masonry hanger had to be nailed to prevent the lower half of the joist from twisting and thus promoting floor flex.

 

I think that's true for hangers fitted to a timber wall plate. The pictures of masonry hangers show no nail holes on the bits facing the wall. 

 

http://www.strongtie.co.uk/products/detail/heavy-masonry-hanger-for-solid-joists/341#tab-installation

[Temp]

1 hour ago, epsilonGreedy said:

There is however another aspect mentioned in the Posijoist manual, they say if joists are expected to contribute to lateral wall bracing special hangers are required. I wonder if these require nailing.

 

NHBC have a lot on floors and joists in their site work guides..

http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2011/Part6/section4/sitework.htm

 

Builders merchants are full of bent bits of metal for this sort of thing. I think you normally use a L shape strap hooked over the wall and nailed to the joist in addition to the hanger. One of these straps every 2m. Something like that.

 

PS: If it's different for Posijoists I would ask them.

 

Edited March 21, 2018 by Temp

[StructuralEngineer]

The timber to masonry hangers in this list all have a ledge which sits in the bed joint:

http://www.strongtie.co.uk/products/gamme/timber-to-masonry-hangers/129/liste

[Moira Niedzwiecka]

@Luckylad

I have found the same with celcon blocks cracking.

I have used them bedded on to the beam & block ground floor to erect the internal stud timber walls on as I thought it would be less of a cold bridge.

[ToughButterCup]

23 minutes ago, StructuralEngineer said:

The timber to masonry hangers in this list all have a ledge which sits in the bed joint:

http://www.strongtie.co.uk/products/gamme/timber-to-masonry-hangers/129/liste

 

Yeah, that's all well and good.

But with a screen name like yours, we all want to know what YOU think 

 

(We'll keep your answer private)

[Gone West]

4 hours ago, epsilonGreedy said:

 

There is however another aspect mentioned in the Posijoist manual, they say if joists are expected to contribute to lateral wall bracing special hangers are required. I wonder if these require nailing.

 

My metal web joists hang on a ledger plate from the top chord.

[epsilonGreedy]

42 minutes ago, StructuralEngineer said:

The timber to masonry hangers in this list all have a ledge which sits in the bed joint:

http://www.strongtie.co.uk/products/gamme/timber-to-masonry-hangers/129/liste

 

 

Thanks, this video from the StrongTie web site helped and now I can picture how the ties work as well though did anyone notice show they skipped nailing the tie to the wall block, is that an error in the video creation?

 

p.s. Do people find these auto enhanced YouTube inserts annoying?

 

 

Edited March 21, 2018 by epsilonGreedy

[Mr Punter]

25 minutes ago, epsilonGreedy said:

Thanks, this video from the StrongTie web site helped and now I can picture how the ties work as well though did anyone notice show they skipped nailing the tie to the wall block, is that an error in the video creation?

 

p.s. Do people find these auto enhanced YouTube inserts annoying?

 

Do don't nail to the blockwork.  The courses above keep it in place.

[Luckylad]

2 hours ago, Moira Niedzwiecka said:

I have found the same with celcon blocks cracking.

@Moira Niedzwiecka

ive got a photo of my neighbors house which is 6 years old ,where you can actually see the heat escaping from the cracks in lightweight blocks. You can also see cold bridging and missing insulation!

[MikeSharp01]

19 minutes ago, Luckylad said:

ive got a photo of my neighbors house which is 6 years old ,where you can actually see the heat escaping from the cracks in lightweight blocks. You can also see cold bridging and missing insulation!

You should get that picture with an IR camera, that will give your neighbours something to think about! Several of us here, following a recommendation from @JSHarris, have this one 

  Although I do not remember paying the sort of prices I see they are today. Also FLir now have a similar one.

Edited March 21, 2018 by MikeSharp01
Typo

[Moira Niedzwiecka]

@Luckylad

Wow,

Not good.

I am glad I have only used a single course with a DPC both under the block & on top before the timber stud walls were erected.

I will make sure that the DPM is well sealed to the DPC & the floor insulation is tight up against them.

I used them because they are supposedly more thermally efficient than standard concrete blocks.

When they arrived from the builders merchants on a small pallet several were already cracked or in pieces.

[Declan52]

I used lightweight blocks on mine and have had no cracks. Have also covered the house using my seek camera and it was fine. 

Are you sure the heat is escaping because of the blocks and not due to dot and dab thermal tent on the inside.

[Luckylad]

They are more thermally efficient on paper but not in the real world.

The 2 wet looking patches that fall away from the upper window are cracks that can easily be seen in daylight ,the lighter coloured areas had frost on them.

glad to hear that about your walls @Declan52, could you give me a detailed breakdown of them please?

mine have got bed joint reinforcement, which was a bit like a toy train track.

that camera looks the dogs dangles!

[Declan52]

Used a standard block on the outside skin then a lightweight on the inside skin. I drenched the lightweight blocks then put on the scratch coat then skimmed and painted it up. In my house 3 1/2 years now and it's hardly any cracks. 

If there is that much heat escaping then the problems are on the inside skin and poorly installed cavity wall insulation not the outside cracks. 

The seek camera is a really good tool to have. 

[StructuralEngineer]

20 hours ago, recoveringacademic said:

 

Yeah, that's all well and good.

But with a screen name like yours, we all want to know what YOU think 

 

(We'll keep your answer private)

 

I think Simpson Strongtie have a great technical department whom I've used several times in the past, and they have always been able to fully justify why they're recommending any of their product range. The problem comes when copycats produce almost the same product, but forget to see the small but vitally important little folds or webs in the metal. Take for example the raised area on the fold of the following hanger:

It stiffens the folded sheet metal, and if it's missing, the metal may unfold under the weight of the floor. It's exactly like a steel tape measure -- consider how easy it is to bend one way and difficult the other way.

 

Regarding joist hangers for I-section joists, really this is the domain of the joist suppliers, since they're the ones that warranty the system, and the hangers are a vital part of the system. Again the issue here is that Posi-joist are highly technically astute and provide the following detail, but copycats may forget to include one vital part of the system (can you spot it @recoveringacademic?).