Trusses against brick wall

[MortarThePoint]

We have a lower level roof (half flat half pitched) that the designer has used JHI masonry hangers to attach to the wall at one end (circled below). The wall is already built and I was wondering if people thought cutting a masonry joist hanger in to an existing wall is harder than using a ledger board and timber joist hangers?

 

[MortarThePoint]

This is what I mean by a ledger board:

[Temp]

I think most masonry hangers require a minimum number of ??  brick/block courses above them.

[MortarThePoint]

Just now, Temp said:

I think most masonry hangers require a minimum number of ??  brick/block courses above them.

 

That's prior to loading, they can be built in during construction. The wall extends a storey higher.

[Mr Punter]

Your ledger board will restrain the walls better.

 

With the masonry hangers would you be chasing out some of the mortar join?

[MortarThePoint]

1 minute ago, Mr Punter said:

Your ledger board will restrain the walls better.

 

With the masonry hangers would you be chasing out some of the mortar join?

 

Yes, I'd have to cut out some bed and then mortar the hanger in which doesn't sound much fun

[Mr Punter]

You may want to use a mortar resin or a strong mix in a pointing gun if you chase the joints out.  Make sure you vacuum them first.

 

An apt user name!

[MortarThePoint]

28 minutes ago, Mr Punter said:

You may want to use a mortar resin or a strong mix in a pointing gun if you chase the joints out.  Make sure you vacuum them first.

 

An apt user name!

 

Drilling holes and using Rawlbolts feels like an easier process.

[Russell griffiths]

You generally fit them with an angle grinder instead of drilling out the mortar. 

Get the hangers that also have flanges on the sides to take bolts. 

 

Draw a straight line across the wall and do a series of deep grooves the thickness of the cutter blade, you will find the flange on the hanger is about the same thickness 2-3mm, hammer in the hanger with a club hammer, when all plumb and lovely add a bolt to each side flange. 

[MortarThePoint]

6 minutes ago, Russell griffiths said:

You generally fit them with an angle grinder instead of drilling out the mortar. 

Get the hangers that also have flanges on the sides to take bolts. 

 

Draw a straight line across the wall and do a series of deep grooves the thickness of the cutter blade, you will find the flange on the hanger is about the same thickness 2-3mm, hammer in the hanger with a club hammer, when all plumb and lovely add a bolt to each side flange. 

 

That sounds good. Do you know of any brands that make that type to help me find them? They sound like they are designed to avoid the need for mortar or resin with the tab that tucks into the brickwork.

[Russell griffiths]

If you use this type you can just bolt on. 

[MortarThePoint]

1 minute ago, Russell griffiths said:

If you use this type you can just bolt on.   [Simpson SAE]

 

Yes I saw that type when looking just now and that doesn't have any tabs that tuck in. I like the sound of the hybrid approach you described as that seems like the best of both worlds.

 

The SWL (probably 2.2kN aka 220kg) isn't particularly good which is a shame [datasheet]. The tuck in type have about 3x the SWL [their datasheet].

 

[MortarThePoint]

Interestingly, the SAE hangers are not listed on the "Timber to Masonry Hangers" page of the Simpson StrongTie website. The SAE page and datasheet and don't mention masonry except for one picture. The datasheet was updated on 10 March 2021!

[MortarThePoint]

I spoke to Simpson StrongTie and they said the masonry application is still possible, but they found it raised more questions than it was worth and they preferred it to involve an Engineer. For example worries that people may bolt them into a bed rather than mid block/brick.

[MortarThePoint]

Saberfix are a bit more optimistic about the SWL with their product. Seem hard to find for 38mm trusses/joists (Screwfix only sell the 50mm ones annoyingly).

 

 

[Oz07]

Just use a board way easier. 

[MortarThePoint]

3 minutes ago, Oz07 said:

Just use a board way easier. 

 

Yes I'm going to go that way. I also saw that he NHBC says that masonry hangers shouldn't be cut "into the walling" I presume that means shouldn't be retro fit rather than saying it shouldn't be cut in to the block itself. Also, some other warranty providers stipulate that materials shouldn't be mixed in the area and I have a transition from blockwork to brickwork at this level.

 

Just need to decide my ledger board size. At one end of it I am going to rest it on the wallplate of a perpendicular wall as well. If I had thought about t more, I could have built it in to the wall at the other end as well but that's not a big issue. 

 

https://nhbc-standards.co.uk/6-superstructure-excluding-roofs/6-4-timber-and-concrete-upper-floors/6-4-13-joists-into-hangers/

 

https://9329f7a9-f105-4a46-b2bc-a658e29c21db.filesusr.com/ugd/981144_d12f36e2d1bb4fe78f9179e65dd7981f.pdf

[MortarThePoint]

All that said, and here is a retrofit specifically for thin joint. Not relevant to me but thought I would add it for completeness:

 

 

[PeterW]

28 minutes ago, MortarThePoint said:

I also saw that he NHBC says that masonry hangers shouldn't be cut "into the walling" I presume that means shouldn't be retro fit rather than saying it shouldn't be cut in to the block itself.

Ignore the NHBC. They say a lot of things that go against the MIs and in the end it will be a question of whether you’ve followed the MIs rather than a trade body if things go wrong. 
 

I would be using a strongly restrained fixing in your case as there is more of a rotational pull on those mountings as the truss will try and pivot on the wall plate and the top mounting. 

[MortarThePoint]

5 minutes ago, PeterW said:

I would be using a strongly restrained fixing in your case as there is more of a rotational pull on those mountings as the truss will try and pivot on the wall plate and the top mounting. 

 

I don't see what you mean. tipping of the hanger side to side? There isn't a top mounting just bracing.

[PeterW]

1 hour ago, MortarThePoint said:

 

I don't see what you mean. tipping of the hanger side to side? There isn't a top mounting just bracing.

so your truss will rotate about the fixed point. The wall plate on the right is static (red triangle) the weight of the truss will try and push downward but rotate around its axis so there is a pull force exerted on the fixings of the bottom chord and it will try and push itself past the wall plate. 
 

Crude arrows below ..!!

 

 

[Gus Potter]

Hi MortarThePoint.

 

The ledger option can work well but as Peter points out you get this twisting effect.

 

Often you get stuck with ledgers as you stuggle to get the fixing capacity. Many fixings are rated on, not least, being fixed away from the mortar bed etc. If you have perforated bricks say the capacity of the fixings really drops off. Expanding type anchors don't work well in perforated brick and there is little test data available.

 

I have attached a very quick sketch showing another way of doing this where you extend the bottom chord and pocket the wall. You can add glued hardwood packers to level up. Here you get a good solid bearing on the masonry and by using the dwangs / noggings you can add extra horizontal tying of the trusses into the existing wall.

 

You may need to beef up the bottom chord a little as it is acting in shear rather than bearing.

 

 

 

 

 

[Oz07]

Not a bad shout @Gus Potter keeping it simple and doing away with fixings and metalwork. Could make it work to course height

[Gus Potter]

Thanks Oz07.

 

This can work out as a simple solution. If you are doing it DIY then it can work well. You can chain drill the pockets with an SDS drill, take your time, avoid dropping a lot of fragments down the cavity (if you have a cavity wall) while getting the pockets pretty level.

 

Also, with a horn like this you get a little more play in the trusses. Say the wall you are joining onto is not straight then you can move the trusses a little horizontally so the rafters of the trusses plane nicely. Often you get the horn a little longer then trim on site to suit.

 

With the hanger option you often find that the nails for the hangers (or hangers themselves) clash with the truss nail plates and intuitively we know that if you have too many nails in a bit of timber this is not a good thing.

[MortarThePoint]

20 hours ago, PeterW said:

so your truss will rotate about the fixed point. The wall plate on the right is static (red triangle) the weight of the truss will try and push downward but rotate around its axis so there is a pull force exerted on the fixings of the bottom chord and it will try and push itself past the wall plate. 
 

Crude arrows below ..!!

 

 

 

Thank you for the consideration and the diagram! I think it will only try to pull laterally if the top vertical left hand member in the diagram contacts the wall, which it doesn't. That vertical member is 25mm nominal from the wall so the only member contacting static points is the bottom chord at the wallplate (R) and at the hanger (L).

Edited April 4, 2021 by MortarThePoint