Can I get a buy, - or construct a load-bearing door frame?

[Howie]

Hi all,

I want to knock through an internal wall to make a new doorway, and (ideally) what I'm looking for is a ready made doorframe or door/frame unit which will support 3 floor beams above it.

The reason for this is that I haven't got a wall on one side to sit a cross-beam on. I have considered making a filtch beam which can cantilever over the doorframe and support the beams above, however, I still feel that there may be some slight movement or creaking. I have done a (fixed width font) ascii drawing below, to illustrate the problem. As you can see, there is no means of support on the left hand side. (The left hand side is actually the void where a self-supported staircase stands).

3 floor beams... || || || || || || single brick wall _ _ _ _ _ _ _ _ _ |_|_|_|_|_|_|_|_|_ ________________ |_|_|_|_|_|_|_|_|_|_ | | |_|_|_|_|_|_|_|_|_|_ | | |_|_|_|_|_|_|_|_|_|_ | top of | |_|_|_|_|_|_|_|_|_|_|_ | door | |_|_|_|_|_|_|_|_|_|_|_ | | |_|_|__|_|_|_|_|_|_|_|_ | | |_|_|_|_|_|_|_|_|_|_|_|_

Any advice or suppliers info would be greatly appreciated!

Regards,

H.

[Lurch]

On Thu, 16 Dec 2004 13:29:59 +0000, Howie strung together this:

Erm, no. You're going to have to get a structural engineer in to have a look at this, sounds like you already know that though.....

[BigWallop]

First you'll need a structural engineers advice. Then you'll need technical drawings of how the new structure will withstand the loadings and materials to be used that the engineer has calculated. Then you'll need planning permission from your local authority before carrying out any of this type of works.

An engineer will know if the existing structure is holding anything else in place, and if it can be removed or replaced safely. This might not be as straight forward a job as you might think it is. Cantilevers aren't always the best things to use to hold your house up.

[John Rumm]

The drawing you can do yourself as a sketch. The calcs are not that difficult in this circumstance. You could produce all the calcs in the demo version of Superbeam.

Unless this is a new front door in a new position, I don't think it is likly he will need PP. I doubt he would even need a full plans submission to the BCO. A building notice would probably be more than enough.

I don't see any need for a cantileaver, so long as you can build a decent set of studs to either side of the door, they can then carry a cross member to pickup the joists above. So long as there is a decent foundation to take the load you should be fine. All you are in effect doing is replacing one section of wall with another of a different construction.

[BigWallop]

The point about there being "three floor beams", which I take to mean joists, means to me that this isn't going to be a small opening. That's unless the joists are very close together, which then also means the floor above is taking a bit more than normal loading.

If the joists for the floor above are all resting on this original wall, it surely means that this wall is a main supporting wall in some way. To remove even small parts of it, which, by the description given, sounds to be of a solid masonry construction, and replace with a simple timber door frame, isn't something to be taken lightly. A simple timber door frame isn't strong enough to take the place of main joist supporting masonry in no way, and the OP may need more substantial timbers, or even steel, to take the place on the original brickwork.

I'll stand by my first reply of advising a structural engineer giving proper advice on this one.

[John Rumm]

Three beams to me suggests a gap of 800mm c/c at normal joist spacing. About the width of a normal door frame.

A stud wall can be load bearing, there is nothing mystical about a single course of bricks. You might be supprised by just how strong a timber frame can be, especially under compression.

A few back of envelope calcs should give you a feel for it. Say the floor joists above were 4m in length. Ordinary bedroom say, with a typical loading of 0.8kN / m. That will give you a down force of 1.6kN at the wall for each joist. Multiply by three since there are three of them, giving a total load of 4.8kN or approx the same as supporting 480kg.

That give two questions, how strong does the crossmemeber need to be at the top to pickup the load of the middle floor joist at the centre of its span, and how strong do the sides of the door frame need to be to take the total load in compression.

A fiddle with superbeam shows that a crossmember of 100x100 (i.e. a couple of 4x2"s side by side) will exhibit a total deflection of under

1mm and well inside the limits on shear stress. Assume the vertical posts are 2.4m long, use a pair of 4x2"s for each side, sharing half the 4.8kN load each. You get compressive stress of 0.24 N/sq mm where the maximum permitted for bog standard c16 timber would be 3.33, so again loads of margin, and that is before you put in the door lining and any other noggins.

Nothing wrong with that bit of advice, although I also expect with a little research you could do it yourself. It would get more complex if the floor above was picking up other loads (like load bearing walls), but only carfully looking at the structure and layout will answer that.

[BigWallop]

So you did the calculations and found a difference in the thickness of timber needed for a safe installation. The OP (Howie) was asking if he could replace the slapping with a normal timber door frame. You're own calculations above show this to be unsafe because a normal timber door frame isn't thick enough to support the floor joists at the theoretical span you've used for your equations.

What if the total span of the joists in Howies house floors are actually one meter longer than you've used in your hypothetical calculations? You don't know what setup is in Howies house, so it is not a very good idea to say yes go ahead and do it the way you want to. If the OP had given total span length, joist spacing and more details of what else is above the joists on further floors, then maybe we could have given more in depth advice. But as it stands, there isn't enough information to be able to say it will be safe.

[Roger]

The message from John Rumm contains these words:

I am a bit puzzled why the op should want to go down the massive doorframe route. What is wrong with a standard doorfame (which would mean a narrower opening through the wall itself) with a suitable lintel above?

[Mike]

Because there was no structural wall capable of taking the load on one side of the door.

[Roger]

The message from "Mike" contains these words:

I overlooked/forgot that. Probably on account that I can't visualise knocking a hole through a wall when there is no wall left one side of the hole. Anyway the solution only requires pillar that side of the hole, not both sides.

[Rob Morley]

Assuming the joists are on standard 14" centres the opening only has to be 26" to be supporting three of them, and that's narrower than a regular door opening.>

I'd just frame it with sawn 4x4, tack expanded metal lath on the sides for plastering, and line it with a bit of planed timber. Unless there's a lot of brick sitting on top of it as well as the joists, in which case it will probably need steel.

Where's your sense of adventure? :-)

[Mike]

Yes, but I think a four sided steel rectangle would spread the load into the floor more evenly and wouldn't need driving in as deeply as a single pillar. However he needs a structural engineer to see it in real life to make a final decision.

[John Rumm]

I think you may be reading too much into Howie's OP. I got the impression that he wanted to know what sort of construction was required to carry the load, and if it could be incorporated into the door frame, or if some form of cantilever into the brickwork would be viable.

Not really, since I did not have any preconception as to what a "normal" door frame is, since a frame is typically built from several components. Perhaps you do, or perhaps you are thinking of only a door lining (i.e.

5x1" PAR timber side and top rails)?.

Given there was no supporting structure to the left of the proposed door, a frame would need to be built to take the load. The simplest frame to build is timber. Hence my first guess was a pair of 4x2"s side by side which seemed like a nice easy size to work with for a stud wall given the typical thickness of a door lining (it should also match the single course or bricks for thickness)... As it turned out these were more than good enough - at least given the other assumptions I made.

Unlikely to be that far out (800mm c/c joists would be unusual), but the proposed beam is still OK even at that length, as it happens... ;-)

My calcs were not intended to be a full design, hence the comment about a back of an envelope exercise. You will also note that I pointed out careful analysis of the existing structure would be required to arrive at a complete answer.

I think the thrust of what I was saying was rather than blindly go the route of a structural engineer and a full plans (or even PP!) application which will likely leave you 600 quid worse off before you have even started, you could DIY these aspects since they are not rocket science, and easily within the grasp of someone with a practical approach, who is prepared to do a little planning and research. The choice will obviously be a decision for the OP.

Agreed. By the same token your assertion that "A simple timber door frame isn't strong enough" is also not based on enough information to say with any certainty.

Perhaps Howie could provide a bit more information?

[Howie]

|BigWallop wrote: | |> The point about there being "three floor beams", which I take to mean |> joists, means to me that this isn't going to be a small opening. That's |> unless the joists are very close together, which then also means the floor |> above is taking a bit more than normal loading. | |Three beams to me suggests a gap of 800mm c/c at normal joist spacing. |About the width of a normal door frame.

Actually the beams at this point are 410 on centre, but the 3rd one (where there will be no supporting wall), is only 220mm as this is where the staircase restricts the width.

| |> If the joists for the floor above are all resting on this original wall, it |> surely means that this wall is a main supporting wall in some way. To |> remove even small parts of it, which, by the description given, sounds to be |> of a solid masonry construction, and replace with a simple timber door |> frame, isn't something to be taken lightly. A simple timber door frame |> isn't strong enough to take the place of main joist supporting masonry in no |> way, and the OP may need more substantial timbers, or even steel, to take |> the place on the original brickwork. | |A stud wall can be load bearing, there is nothing mystical about a |single course of bricks. You might be supprised by just how strong a |timber frame can be, especially under compression.

Hmmm, yes. This is why I was wondering if I could incorporate some load-bearing into the door frame, -possibly supporting a (then only semi)-cantelevered beam across the top of the existing brick wall. | |A few back of envelope calcs should give you a feel for it. Say the |floor joists above were 4m in length. Ordinary bedroom say, with a |typical loading of 0.8kN / m. That will give you a down force of 1.6kN |at the wall for each joist. Multiply by three since there are three of |them, giving a total load of 4.8kN or approx the same as supporting 480kg.

Again, this is almost exactly how it is laid out. how did you know? !!! | |That give two questions, how strong does the crossmemeber need to be at |the top to pickup the load of the middle floor joist at the centre of |its span, and how strong do the sides of the door frame need to be to |take the total load in compression. | |A fiddle with superbeam shows that a crossmember of 100x100 (i.e. a |couple of 4x2"s side by side) will exhibit a total deflection of under |1mm and well inside the limits on shear stress. Assume the vertical |posts are 2.4m long, use a pair of 4x2"s for each side, sharing half the |4.8kN load each. You get compressive stress of 0.24 N/sq mm where the |maximum permitted for bog standard c16 timber would be 3.33, so again |loads of margin, and that is before you put in the door lining and any |other noggins.

That's helpful. Thanks. (I must have a look at Superbeam. Never tried it before). | |> I'll stand by my first reply of advising a structural engineer giving proper |> advice on this one. | |Nothing wrong with that bit of advice, although I also expect with a |little research you could do it yourself. It would get more complex if |the floor above was picking up other loads (like load bearing walls), |but only carfully looking at the structure and layout will answer that.

All other walls on the above floor are stud, and do not rest on any of the three beams in question.

John, may I thank you for a really helpful, comprehensive reply.

Regards, Howard.

[Howie]

|BigWallop wrote: | |> So you did the calculations and found a difference in the thickness of |> timber needed for a safe installation. The OP (Howie) was asking if he |> could replace the slapping with a normal timber door frame. You're own | |I think you may be reading too much into Howie's OP. I got the |impression that he wanted to know what sort of construction was required |to carry the load, and if it could be incorporated into the door frame, |or if some form of cantilever into the brickwork would be viable.

Yes, I was. :-)

|> length, joist spacing and more details of what else is above the joists on |> further floors, then maybe we could have given more in depth advice. But as |> it stands, there isn't enough information to be able to say it will be safe. | |Agreed. By the same token your assertion that "A simple timber door |frame isn't strong enough" is also not based on enough information to |say with any certainty. | |Perhaps Howie could provide a bit more information?

See previous reply to your last post.

It may be worth mentioning that there is no other loading on these 3 beams. The rest of the beams layout is either at 90' to them or has stud walls lying over different beams on the same floor.

[Howie]

|The message |from John Rumm contains these words: | |> A fiddle with superbeam shows that a crossmember of 100x100 (i.e. a |> couple of 4x2"s side by side) will exhibit a total deflection of under |> 1mm and well inside the limits on shear stress. Assume the vertical |> posts are 2.4m long, use a pair of 4x2"s for each side, sharing half the |> 4.8kN load each. You get compressive stress of 0.24 N/sq mm where the |> maximum permitted for bog standard c16 timber would be 3.33, so again |> loads of margin, and that is before you put in the door lining and any |> other noggins. | |I am a bit puzzled why the op should want to go down the massive |doorframe route. What is wrong with a standard doorfame (which would |mean a narrower opening through the wall itself) with a suitable lintel |above?

This would mean building a free-standing pillar on top of the foundation wall to support the other end of the lintel. Otherwise, there really isn't anything structural to rest it on. all I have is a stud casing around a free-standing staircase.

[Howie]

|I'd just frame it with sawn 4x4, tack expanded metal lath |on the sides for plastering, and line it with a bit of planed timber. |Unless there's a lot of brick sitting on top of it as well as the |joists, in which case it will probably need steel. | |> I'll stand by my first reply of advising a structural engineer giving proper |> advice on this one. |> |Where's your sense of adventure? :-)

Thanks Rob. Perhaps I have too much sense of adventure and an excess of bravado! I'd really like to do this work myself though.

I've just had another look at it and I reckon I could change my other plans to incorporate a stud wall underneath these 3 beams. BUT it would be 1.4metres away from the ends I'm exposing. I suspect that this, - combined with your proposed 4x4 reinforced frame, will be fine.

H.

[John Rumm]

Fair enough.... in the ball park of the gusstimate then.

Ah, the cantilevered section you are refering to is presumably what is called the "wall plate" (i.e. a timber "cap" that runs along the top of the wall on which all the joists in turn rest). This is there to spread out the point loads on the masonry. Once your change is implemented, it will still be supported along its full length (partly by the wall and partly by the studwork), and hence not actually cantilevered.

In good Blue Peter tradition, here was one I made earlier... (i.e. I already had a model in superbeam for the floor joists in one of the rooms in the loft conversion I just built). That was a 4m span and seemed a reasonable guess. In fact a couple of meters either way would not make much difference since you are typically talking about a change of only 400N (i.e. 800N total shared equally between the two ends) down force at one end of the beam for each extra meter span.

Its a nice bit of software, but can be a bit intimidating at first glance. It does assume a certain amount of background knowledge. In particular knowing what sort of loadings to specify in various situations. (The 80kg per linear meter on a floor joist is pretty common

- the BCO accepted all the calcs without query).

In many cases "gut feel" will get you a design that is in all likelihood over engineered anyway, using the software as a sanity check can give you peace of mind, and send a BCO away with his tail wagging.

That makes it quite easy then. The only load on your wall will be due to the floor load on the beams.

Ta! In some ways it was more intended to counter the "wetness" of some of the replies you were getting ;-)

[Howie]

|> Hmmm, yes. This is why I was wondering if I could incorporate |> some load-bearing into the door frame, -possibly supporting a |> (then only semi)-cantelevered beam across the top of the existing |> brick wall. | |Ah, the cantilevered section you are refering to is presumably what is |called the "wall plate" (i.e. a timber "cap" that runs along the top of |the wall on which all the joists in turn rest).

Well, yes. Although there isn't one there ATM. I plan to put one in myself.

|This is there to spread out the point loads on the masonry. Once your |change is implemented, it |will still be supported along its full length (partly by the wall and |partly by the studwork), and hence not actually cantilevered.

Not exactly of course, no. I was using the term because _some_ of it's strength could come from the fact that approx 3/4 of it will be resting on the wall and the overhang is in turn being supported by the framing I am proposing. Of course, that will also help give some additional lateral strength to the new doorframe.

I am usually guilty of trying to apply my version of a commom-sense approach to these jobs, - along with a bit of obviously over-engineered DIY work. It worked really well for the people who set the beams on our house in France 300 years ago and I reckon it's not a bad philosophy to follow!

|In many cases "gut feel" will get you a design that is in all likelihood |over engineered anyway, using the software as a sanity check can give |you peace of mind, and send a BCO away with his tail wagging.

So I see you have a similar approach, - but with much more knowledge!

|That makes it quite easy then. The only load on your wall will be due to |the floor load on the beams. | |> John, may I thank you for a really helpful, comprehensive reply. | |Ta! In some ways it was more intended to counter the "wetness" of some |of the replies you were getting ;-)

And very gratefully received it was too. Don't get me wrong, - I value all replies anyway. Examining a consensus and filtering out the obtuse, especially in this group, has helped me in many ways previously. I am never less than pleased with most questions I ask. I am gradually finding that I am also occasionally able to help others with their questions. Eventually, it would be nice to achieve parity of knowledge and therefore usefulness! That's what it's all about IMO.

Best regards, - and seasonal felicitations to all contributors.

Now.... where's my lump-hammer?

;-)

H.

[John Rumm]

If there is not one there now, then there is no need to have one. Just build your new wall to the same finished height as the existing one. (only becomes a big issue with steel or other small contact area beams onto soft light weight blocks).

If you wanted you could build a much thiner frame on the side that butts against the wall since you could take the cross memeber directly into the brickwork if you wanted by taking out the top brick. (you can use bits of slate on the top brick (under the end of the cross member) to get the height just right if required.

Yup, we do obtuse well here ;-)

And you...

Don't forget the Acrow!