Dimensions of a wooden lintel over a window

[Lucky Luke]

I was looking for a way to securely fix holding-brackets, for a venetian blind, to the top of our lounge window recess. At the moment, all that could take the screws for these brackets, if fixed at the top, would be three-eighths plasterboard, while, at the side of the window aperture (its walls, so to speak), there is a void behind the plaster where the brackets might otherwise have been fixed. (I tried drilling through, and found nothing but plaster.)

Anyway, a friend advised me that above the window will be a wooden lintel (he said that it would provide a three inch wide corridor of solid timber, to drill into and fix a board to with longish screws, staggered across the three inches. Then, the brackets could be fixed further away from the lintel (i.e. much nearer to the window frame). He assures me that this would be a safe way of fixing the board, despite the non-screwed part of the board overhanging (so to speak) the line of staggered screws that will be driven through the board and into the lintel. It sounds good. However, can anyone kindly offer an informed opinion as to the minimum thickness of board that I ought to fix? And whether, over time, the non-screwed portion of the board might bend, because of repeated raising of the blind, and its weight generally?

Another thing that has set me wondering also, is this: the friend said that the lintel will be three inches wide. Yet, above this lintel, and resting upon it, is a brick wall (this goes up from the lintel to the underside of the bedroom window above it). Now, surely, that brick wall will be four inches thick. How is it, then, that at best, it must overhang half an inch over each side of the lintel (or else a full inch over one side only). Ought not a lintel to be at least as wide as the bricks resting on it? What dimension will the lintel be as to width and height? Might my friend have been mistaken, with his three inches estimate?

This house was built in about 1947, by the way.
With thanks in anticipation of helpful feedback about the various questions raised here,
A.W

 

[tony1851]

Timber lintels are normal in older houses.
They are generally 4" wide (if in a cavity wall) rather than 3".
The depth of the lintel will depend on the span. There was an old rule of thumb for timber lintels in brick walls which went: 'depth in inches = span in feet'.
Just screw your board into it and it will be fine.

 

[Lucky Luke]

Thanks for that, Tony. I omitted to say that the span of the window is about seven foot six, while the depth of the window recess is eight inches. From what you say, the brackets will be only about two inches away from the lintel's edge.

I am thinking of buying a plank of planed Swedish redwood for the board. It will be seven eighths thick. I would like to buy three-quarter inch plywood, but I should have to buy the full eight by four board, so cost would be prohibitive.
A.W.

 

[theprinceofdarkness]

1947, could easily be a concrete lintel, which will be a devil to drill into. I think you have to bite the bullet and find out what is going on. You seemed to have drilled a hole, put a nail through the hole and tap it, to find out what the lintel is and with a piece of clothes hanged wire make a probe to find out where its bottom edge is, it could be 1 1/2" above the top of the window recess. If the "plaster" is actually skimmed plasterboard, it will be fitted to battens, try with a metal detector to find the plasterboard fixings, this is where the bottom front edge batten is, you can fix to this.
Frank

 

[Lucky Luke]

Tony (and anyone else that may like to chip in: By making fine exploratory, fine-bore drillings, I have discovered that, whereas I thought there would be a wooden lintel to which the inside edge of this ceiling plasterboard would be nailed, there is NOTHING THERE! What the edge of the plasterboard is fixed, I cannot imagine. However, I have found absolutely no evidence of even a rail, to span the width of the window aperture.

Setting that aside, what I have found out (by enquiring of the man that did the following job for me, about nine years ago) is that underneath the OUTER skin of bricks between this lounge window and the bedroom window above it, is what the tradesman describes as a Catnic lintel (metal). Because of the paucity of solid material, to screw up into (to hold the board that I intend to cover the recess ceiling), I was wondering whether it would be feasible to drill up into this metal lintel, and thus fix the back edge of the board securely. The trouble is, I don't know how far it might project (flat) from the inside face of the outside skin of brick, before going, at an angle, across the cavity. Anyone familiar with Catnic lintels will know what I mean, and what my dilemma is (it would be hard to drill into a metal fitting that slopes at about 45 degrees).

Does anyone have any reasonably accurate knowledge of how much flat metal there might be projecting, of this lintel, so that I could drive self-tapping screws through the new wooden board, the plasterboard, and finally, the metal of the lintel?

I would be very grateful for some helpful feedback. This job is driving me crazy! (However, on the positive side, the board has been cut and shaped, and fits the recess ceiling perfectly. And I made makeshift, adjustable props to hold it in position against the ceiling. They work beautifully!)
With thanks in anticipation,
A.W.

 

[theprinceofdarkness]

catnic lintels are box section. They can have different sections. Mostly they have a "shelf" sticking out the front, on which the outside brickwork sits in. Then there can be a square section and the internal skin starts on top of this bit. So exactly behind the inside of the lintel there is nothing other then the overlaps of the bottom and top. Some catnics have this area covered in mesh so it can be rendered level with the inner skin brickwork. The whole area can then be plastered. Could be that your situation is that the plasterboard was dot and dabbed on (urgh!!)to the brickwork above the lintel and the horizontal strip "glued" to what ever and the edges held together with the edge bead, before it was plastered.
Frank