Lowering ceiling - increasing attic height / adding beams etc

[Username_Here:]

Hey everyone.

Long time lurker here but I've only just signed up.

****
tldr;
I want to lower my ceiling using steel beams on party walls to increase attic headroom. The house is stripped out right now, so I have a lot of freedom. Can anyone advise on beam sizes, bearing depths etc?
****

I'm hoping I can get some beermat engineering feedback on a renovation idea here before I approach an architect/structural engineer. My concern is that I'll be overwhelmed and under prepared if I don't do some homework before I consult the experts, so I want to be as well informed as I can be, in advance.

I have an old terraced bungalow that I'll be renovating in the summer and I am considering the option of lowering the ceiling height to increase the usable space in the loft (for a potential usable play area/games room etc). The existing ceiling is 3 metres in height and the attic space is already approximately 2.2m tall. I'm thinking of bringing the ground floor ceilings down to around 2.4m to allow for more headroom in the attic and more usable space towards the eves.

The house itself is around 100 years old and existing joists/rafters are only 3x2'ish (old school timber sizes) and have a 4x3 purlin running the width of the house on either side to support them. The main area of the house is only 5.6m wide by 6.5m deep (there's an additional extension, but that isn't relevant to the plan). It's constructed from 2 leaves of brick with no cavity in between, and the brick is irregular in size and a little on the softer side. There's also a supporting wall (single leaf of the same brick) in the centre, running the width of the house that the joists sit on.

My hope is that I can get rid of the supporting wall in the middle and open up the space, effectively into one large room, while also lowering the ceiling. To do this, I figured I may need to add in some steel to compensate for the wall, and it would ideally run the width of the house instead of the depth, to avoid window/door openings etc. The new joists could hang off this steel beam and pocket into the existing front and rear walls. After researching the span tables, loads etc I came up with a 305x102x25 universal beam to cover the 6.5m span and 9x2 joists.

This brought me to my next set of concerns. As the house is terraced and has party walls either side (party agreements not an issue), would a single leaf of brick (100mm approx) be enough of a bearing surface for a steel beam, or would I need to have the beam penetrate deeper into the wall (on padstones of course)?

Then I was thinking of ways to minimise that 305mm beam height so that I would get more headroom in the attic and I thought about the option of adding 2 or even 3 smaller steels across the width of the house in the same fashion as the above mentioned large single steel beam. My thought was that I would place one under each purlin so that I could build off it with timber framing to support the purlin/rafters, and these would also become the walls of the new attic space. I could then have a 3rd steel in the middle of these two, so I could shorten the span and use smaller timbers (6, maybe 7 inch?) to get more headroom. One of my issues is that I'm not entirely sure how to calculate the required steel sizes when more than one is used in this fashion, and whether the bearing surface depth is acceptable. I can go deeper, as I own next door too, however it’s inhabited and I want to minimise any mess or damage inside if i can.

I'm also considering the use of columns to support the beams, however this would obviously need to be boxed in and would probably be the uglier option in the finished ground floor space.

Would any of you have any feedback on this plan, or have any other possible solutions I haven’t considered yet? I'd also love to hear from anyone who can give feedback on whether my beam sizing above sounds about right, and what beam size I could go with if I used more beams instead of a single one.

Thanks in advance.

 

[^woody^]

Instruct a structural engineer. One that knows about building regulations and party walls too.

 

[tony1851]

On that span and loading, central steel joist could come down to 203 x 133 x 30.
If using more than 1 steel beam, you won't get much smaller than that because deflection will be the determining factor, and it would probably be cheaper to have one beam, rather than 2 slightly smaller beams.
The position of the main beams will also be determined by the position of the stairs.
Floor joists 7x2 C24 if you're not bothered about a small downstand of the steel beam, otherwise 9x2 joists for a flush ceiling.
OK to stick 4" into the party walls with suitable spreaders.

 

[Username_Here:]

On that span and loading, central steel joist could come down to 203 x 133 x 30.
If using more than 1 steel beam, you won't get much smaller than that because deflection will be the determining factor, and it would probably be cheaper to have one beam, rather than 2 slightly smaller beams.
The position of the main beams will also be determined by the position of the stairs.
Floor joists 7x2 C24 if you're not bothered about a small downstand of the steel beam, otherwise 9x2 joists for a flush ceiling.
OK to stick 4" into the party walls with suitable spreaders.

Thanks, that's really useful.

I'm not too concerned by added cost of the steel if it saves headroom though, as I'm going to lose a little due to insulation and a vented cavity. The stairs would be in one of two locations which essentially mirror each other and would easily work with a single central beam. I believe it would also work with 2 beams below the purlins too, but I would have to confirm the headspace above the staircase to be certain. Ultimately I have a lot of flexibility here, as there's no existing stairs to constrain me.

I see your point about deflection. I had been thinking If I go with 2 beams below the purlins then I figured I wouldn't have to worry about the downstand, as they would form part of the attic wall instead of being in the middle, so they'd essentially be hidden (fixed on hangers, flush on the bottom for a flush ceiling below).

When you mention spreaders, are you referring to padstones here, or just in the generic sense? I've also seen cases where 10mm plate was used as a spreader, though I'm not sure how I feel about that option.

Thanks again for the info.

 

[Username_Here:]

Instruct a structural engineer. One that knows about building regulations and party walls too.

I covered that above.