Removing a ceiling

[richardrich79]

One of the bedrooms needs the old lath and plaster redoing. Rather than replacing we would like to do away with the ceiling & expose the eaves.
The bedroom is in the rear of the property which is a terraced house. The rear bedroom has 3 external walls and there is currently NO insulation of any kind. The roof is welsh slate, in good order having beenstripped and renailed with new laths and felt at some stage in its life.
We intend to insulate between the rafters (leaving an air gap) then another set of kingspan retained by timbers attached to the rafters.
Whilst a quarter of the ceiling joists will be retained to form a mezzanine storage loft we don't want to keep all of the remaining joists.
How can I tell if it's ok to remove them?
So far builders have said:
1/ no problem to remove them all.
2/ remove every other one.
3/ keep one central beam but double it up by bolting 2 together.
I thought to remove the existing ceiling joists, cut them in half and replace them higher up either side of the rafter with bolts and gripper washers.
any ideas will be most welcome.

 

[pinenot]

When you speak of removing the ceiling joists, also called ceiling ties because they tie the bottom of the rafters together preventing outward spread through roof load, so before removing these ties what will you putting in in there place? ...pinenot

 

[tony1851]

If it's an old (Victorian?) house, you need to be careful if removing the ceiling joists; you're no doubt aware that they also perform a tying function, preventing the rafters from pushing out on the wall.

 

[richardrich79]

what will you putting in in there place?

That is my question.
The builder we had (don't ask) told SHMBO 'no problem'. I realise the potential removal problem but we have seen examples of rooms where the 'ceiling joists/ties are higher up & that's what she'd like.

 

[pinenot]

Could you post a sketch? ...pinenot

 

[KenGMac]

richardrich79, Hi.

I am concerned about "roof spread"?

Removal of ceiling ties in effect removes the "triangulation" of an element of the roof, if you consider the two rafters on each slope of the roof, plus the ceiling tie as being a "composite" unit, then by removing one of the three elements, the ceiling tie then you run the risk of in effect "loosing" an important restraint.

If you think of a roof, and break it down to a single element that being as above two rafters and a ceiling tie, it is generally accepted that the rafters are in compression, the ceiling tie is in tension, that is the ceiling tie is acting to prevent the two rafters from "kicking out" over the external walls.

OK what about the wall plate? Yes it does provide some "restraint" but when the full load of roof, including Welsh Slate acts on the wall plate, without the assistance of the Ceiling tie then the roof will cause the walls to bulge outward, in effect spread. Provided the wall plate is firmly anchored to the top of the wall?

As for moving the position of the wall plate to a higher position? same problem occurs? There is a possibility that roof spread could occur?

You could leave all of the ties in position, but clean them up and do a rough sand off to them followed by a few coats of varnish and the ties become a "feature"

Lets see what the rest of the board think?

Ken

 

[tony1851]

The problem here is that no-one, not even an SE, can give an unqualified answer as to whether or not the roof would spread. There are so many variables and unknowns that it becomes impossible to answer with certainty.

Factors which affect it are such things as: the degree of fixity at the ridge; the size of the ridge board/beam; the grade-strength of the timber rafters; the frictional force between the wall plate and the top of the brickwork; the length of the roof; the weight of the roof; the quality of the brickwork itself; the height of the wall plate above any lower restraint (such as a floor); and so on

Many of these are unknowns, so put them into the equation and the answer comes out "don't know". It would be a brave/foolish SE who stated unequivocally that there would be no problem in removing the ceiling.

The best answer is; it might work, or it might not.

 

[richardrich79]

Thank's you reinforce what I believe, you can see now why our 'builder' is now our Ex-builder
Once we have the ceiling down and if we go down the route of removing any of the joists we'll first investigate whether to insert a metal-rod type wall tie ( I just happen to know where one's going begging ) 'though really I'm favouring cleaning up & varnish.

 

[pinenot]

Can you elaborate on "expose the eaves and insulation between the rafters, I get two mental pictures" one - that 3/4 of the of the roof you want to be exposed will also be covered in insulation, (or will that only apply to the 1/4 retained as loft storage and hidden from sight?) the second (that - only a section of the eaves, say 1 meter only, will be exposed)
To explain - The eaves of a roof are those sections forming the joint between the rafters and the wall, where the fascias, soffits, wall plates etc. is the make up - per say...pinenot

 

[Blagard]

Reading through the thread some information seems missing, (or I have missed it!). Noting that you want to see the underside of the pitched roof and insulate it. Is the roof a single pitch "lean to" style (anticipated) or is it something else? Do you plan on using plasterboard to the existing rafters, if so what size are the rafters and what is the span (measured along the pitch). If there is a purlin please say so. I have nothing to add to Tony and Ken's comment about the rest of the structure as that seems well covered.

The reason for my questions are that the size of timbers in old properties can vary considerably and they can be well oversize as often as undersize. You don't want to go loading up rafters with additional dead weight without considering the impact.

 

[richardrich79]

Sorry if I've not been clear. the roof is not a 'lean-to' it's pitched. It is a 2 story rear extension to our 3 story terraced house. the rear 'extension' part is not attached to the neighbouring properties & was built at the same time.
There are purlins & the rafters are approx 3" x 2".
The plan is to add kingspan type insulation between the rafters followed by 25mm sheet across held in place by new 'rafters' screwed through the 25mm sheet into the rafters, forming the impression of new rafters. Thin plaster board will then go between the new rafters with a skim coat.
This treatment will be for all the roof up until the wall where it joins the main house. The 'loft' area will be open to the room with access by ladder.
(We have just added a dormer to the existing loft area and building regs required slate, felt, 150mm kingspan, 3-layer foil then plasterboard)

 

[pinenot]

Ah! that's clearer. I'm thinking now somewhat differently, you could consider extending these inner false rafter to form something of a sprocket style roof structure (make these inners like a short sided tent, almost) The section at the internal eaves, so to speak, would have to be beefed up, nut these could be made to add style/charm/design, call it what you will...pinenot