new floor with bolted joist runners and joist hangers

[cs21]

I will be installing a new floor in a room with a vaulted ceiling to create 2 rooms with a new staircase for access to the first floor.  What i intended to do is secure the joist runners on both sides of the room with either rawplug resin chemical threaded fixings or M16 Ancor bolts every 400mm spacing. The joists will also be 400mm spacing hung from joist hangers.  I have been advised that m12 will be sufficient enough for this as there wont be much of a load above the floor apart from bedroom furniture and max two or three people at a time. 

 

Is there any particular joist hangers i need for first floor loads or would the strength of these hangers all be similar in the load capacities they can hold! 

 

I have also been advised by others that ancor bolts can cracks blocks if tightened to much. This would be a major concern of mine if they where to fail. Resin fixings sem to hold up well but its the waiting time and fiddling about getting them exactly into place for the joist runners to sit level that concerns me with this. 

 

Ill be using a 9x2 c16 for the joist and will be getting bolted into a 4inch thick block wall. What length of bolts or threaded fitting should i use. Would 110mm be sufficent. 50mm into the wall, 44mm for the timber and and 16mm for the bolt and washer

 

 

Edited April 29, 2021 by cs21

[George]

These are all questions you need to put to a structural engineer. There are other variables that need to be taken into consideration.

[cs21]

7 hours ago, George said:

These are all questions you need to put to a structural engineer. There are other variables that need to be taken into consideration.

 

 

No structural engineer for this job. Its in my own home and im very confident in doing this to regs and safely 

[Gus Potter]

Hi cs21.

 

Can I suggest that you reflect on the fact that there is a difference between being confident and competant to design and execute the works in a safe structural manner while also keeping an eye on the cost, both short term (the works) and long term.. if you come to sell.

 

George is giving you a heads up that could save you a lot of grief.

 

Yes, you may have managed to size your joists (ten minutes work to get a concept joist size for an SE / competant experienced builder) but there is much more to this than just sizing joists.

 

You are asking about the fixing types, hangers.. no mention as to how your proposals may affect the global building stability. If you are competant then no need to ask the questions you are.

 

I would spend a bit more time mulling this over, a bit more research perhaps?

 

BH is a great place to find the info you need.

 

 

 

 

 

 

[saveasteading]

Don't underestimate how much there is to know about structures. You ask some questions as if there are simple answers, but context and site inspection are essential.

 

Please get this designed by a qualified Engineer. It won't cost a lot, and it sometimes even saves you money.

Building regulations are necessary too.

 

Then you can relax that the fixings won't fail, or the walls crumble,  or that the new stairs are legal etc..

 

When you come to sell, you will be asked for the  proofs, permissions and sign-off, so you might as well do it properly now, then relax. 

 

 

 

[cs21]

On 30/04/2021 at 21:55, Gus Potter said:

Hi cs21.

 

Can I suggest that you reflect on the fact that there is a difference between being confident and competant to design and execute the works in a safe structural manner while also keeping an eye on the cost, both short term (the works) and long term.. if you come to sell.

 

George is giving you a heads up that could save you a lot of grief.

 

Yes, you may have managed to size your joists (ten minutes work to get a concept joist size for an SE / competant experienced builder) but there is much more to this than just sizing joists.

 

You are asking about the fixing types, hangers.. no mention as to how your proposals may affect the global building stability. If you are competant then no need to ask the questions you are.

 

I would spend a bit more time mulling this over, a bit more research perhaps?

 

BH is a great place to find the info you need.

 

 

 

 

 

 

 

 

I do appreciate your concern and advice and i do understand what your saying however, in a 4x4 roof with a maybe 600mm high above the joists in block and the roof load, i cant see where there would be any issues if i have 2 joists runners of 9x2 bolted into the wall with chemical fixings with m16 threaded bar or even m16 raw ancor bolts spaced at 400mm apart with joists of 400mm on joist hangers ever failing if its only loaded out on top with bedroom furniture , osb T&G flooring with either carpet or laminate on top. 

[Gus Potter]

1 hour ago, cs21 said:

 

 

I do appreciate your concern and advice and i do understand what your saying however, in a 4x4 roof with a maybe 600mm high above the joists in block and the roof load, i cant see where there would be any issues if i have 2 joists runners of 9x2 bolted into the wall with chemical fixings with m16 threaded bar or even m16 raw ancor bolts spaced at 400mm apart with joists of 400mm on joist hangers ever failing if its only loaded out on top with bedroom furniture , osb T&G flooring with either carpet or laminate on top. 

Hi cs21.

 

Thanks for responding.

 

This is a bit of a quandary.

 

There are lot's of folk that have building experience that have a feel for what will stand up..it's just that often folk don't consider that we mainly design for a 50 year life span (domestic loadings for dwellings.. flats are a little different) and the loads that have a significant probability of occuring over that time.

 

That is why we have safety factors. We very rarely see a house failing drastically due to over loading alone (I can't think of a case off the top of my head.. there have been some localised floor collapses due to folk hoarding stuff I think).. it's usually due to bad workmanship, changing the specification of materials without consulting the designer/ making what appears to be a small change in say levels of ceiling joists, inadvertantly altering the way the roof trusses work.. suddenly what seems to be a minor change can impact on the loads paths and result in an unstable building.

 

I may have interpreted this wrongly but is the roof already vaulted? If so do you understand how the horizontal thrust from the vaulting roof is resisted. If you are proposing to remove the existing ceiling ties to form the new floor (bottom truss chords say or an existing floor that is set 2 feet down from the wall head that is providing some tying / lateral stability to the existing masonry walls for example) do you fully understand their function and the consequence of removal.

 

Also, have you considered the practical issues relating to how you install the anchors, how they will fit with the coursing both vertical and horizontal so that you maintain the edge distances between the fixings and the mortar joints. Will your runner sit flush with the wall or will it stand off a bit in places if the wall is not straight. If standing off in places then you introduce a bending force into the fixing and this has to be considered. The capacity of some of these fixings can drop off four fold and more depending on the type and condition of masonry you are fixing into.

 

Have a look at the manfacturer's load data and you'll see there is a bit of thinking to do to get this to work. Look carefully at the data as many fixings are only certified for cracked concrete.. not masonry.. even then much is based on EU brick / block sizes not UK sizes.

 

It may be that you just want to cart on based on what you think is fine. But if you pass this house on to relatives or sell to say a young family then you would surely want to know that if they use the house in a different way it will still be safe? Also, say you come to sell and you are asked to demonstrate that what you have done is compliant with the regs in terms of the structure. Will you be able to do this?

 

 

 

 

 

 

[cs21]

20 hours ago, Gus Potter said:

Hi cs21.

 

Thanks for responding.

 

This is a bit of a quandary.

 

There are lot's of folk that have building experience that have a feel for what will stand up..it's just that often folk don't consider that we mainly design for a 50 year life span (domestic loadings for dwellings.. flats are a little different) and the loads that have a significant probability of occuring over that time.

 

That is why we have safety factors. We very rarely see a house failing drastically due to over loading alone (I can't think of a case off the top of my head.. there have been some localised floor collapses due to folk hoarding stuff I think).. it's usually due to bad workmanship, changing the specification of materials without consulting the designer/ making what appears to be a small change in say levels of ceiling joists, inadvertantly altering the way the roof trusses work.. suddenly what seems to be a minor change can impact on the loads paths and result in an unstable building.

 

I may have interpreted this wrongly but is the roof already vaulted? If so do you understand how the horizontal thrust from the vaulting roof is resisted. If you are proposing to remove the existing ceiling ties to form the new floor (bottom truss chords say or an existing floor that is set 2 feet down from the wall head that is providing some tying / lateral stability to the existing masonry walls for example) do you fully understand their function and the consequence of removal.

 

Also, have you considered the practical issues relating to how you install the anchors, how they will fit with the coursing both vertical and horizontal so that you maintain the edge distances between the fixings and the mortar joints. Will your runner sit flush with the wall or will it stand off a bit in places if the wall is not straight. If standing off in places then you introduce a bending force into the fixing and this has to be considered. The capacity of some of these fixings can drop off four fold and more depending on the type and condition of masonry you are fixing into.

 

Have a look at the manfacturer's load data and you'll see there is a bit of thinking to do to get this to work. Look carefully at the data as many fixings are only certified for cracked concrete.. not masonry.. even then much is based on EU brick / block sizes not UK sizes.

 

It may be that you just want to cart on based on what you think is fine. But if you pass this house on to relatives or sell to say a young family then you would surely want to know that if they use the house in a different way it will still be safe? Also, say you come to sell and you are asked to demonstrate that what you have done is compliant with the regs in terms of the structure. Will you be able to do this?

 

 

 

 

 

 

 

 

 

YEs, the vaulted ceiling is already in place. This house was built 20 years ago and is finished. In this room there is a vaulted ceiling where im wanting to make another floor.  From the floor to the peak, its 4.8  high. The rooom is 4x4 square and the slope of the rafters meets the wall plate at 3.1m of the flooring.   Im wanting to install the new flooring at 2.4m high from the floor in this room. Install 9x2 joists, osb flooring and whatever flooring on top of this.   Where i will be installing the joist runners, there will be a few block above this before the wall plate is and as i mentioned above, i intend to install the joist runners every .400mm with either M16 chemical fixings or Ancor bolts or both then joist hangers nailed onto this with the correct fixings. I do very much understand your concern and i do understand floors can collapse under heavy loads but if these runners are installed as i mention, i cant see the life of me how they would fail if its just normal bedroom loading. Is it not how these runners are installed. I could put Rsj's under the joists but  this is over kill IMO. 

[George]

On 30/04/2021 at 20:31, cs21 said:

 

 

No structural engineer for this job. Its in my own home and im very confident in doing this to regs and safely 

 

Well you say that, but all your questions are the more detailed information over and above load/span tables which a structural engineer will help you with. 

 

If building control ask for calculations of the fixings you have used, what will you tell them? Buildhub 'said it would be OK'?

 

Edited May 17, 2021 by George

[PeterW]

Adding to what has been said above, I don’t think there is too much an engineer would want to make this much more of a “designed” solution so wouldn’t be that expensive. 
 

Considerations for you though :

- what sort of blocks are they.?

- can you pocket each end of the wall plate into the wall..?

- where do the stairs enter the room..?

- what provisions are there for fire exit from the above room..?

 

All these will make a difference to the design and the final solution.