How to fasten green oak beams into wall pockets?

[MattJ]

I'm building a porch to connect my back door with my utility room.

It's a 6m beam on three 1.9m oak posts and there's three cross beams to join the main beam to the wall. There'll be a Stonesfield slate roof on it.

I've got dovetails on one end of these cross beams to connect into the main beam, but the other ends of these cross beams will sit in pockets in the wall. I have been contemplating just wedging the beams into the pockets with all the chips of oak I have lying around and then mortaring around beams.

Once I've got everything pegged together, it should be pretty robust, but the oak crossbeams are going to shrink slightly and I'd rather the beams slipped slightly out of the pockets (and I have to re-wedge them) rather than it pull the entire porch towards the wall.

Anyone any experience to share on this?

Matt

 

[middi]

Matt, I am trying to visualise the porch being 6 m long, but how wide is the cross beam span from the support beam to the wall?.

You should not worry too much about any shrinkage along the length of the cross beams , this will be very minimal and after the "settlement" period the tendency will be for the porch to move away from the wall and not to be pulled towards it.

There is no need to wedge the cross beams into the wall, just rest them in the wall by at least 6 inches in depth and point around them with soft mortar, in time there will be shrinkage, distortions, expansions, twisting forces and released and gained stresses in the oak which will lock that lot in a stabilised " permanent" final position.

Just repoint if you need to at the wall end, leave it to it's own devices and enjoy the character.

If you use well seasoned oak, shrinkage will be kept to a minimum, if you use green oak there will be more shirkage and distortions but this is usually better for the interlocking forces that are associated with it.

 

[MattJ]

Here's an old rendering of the porch - this was a test of the CAD package rather than being correct dimensions or showing all the timbers, but it shows the intent. The main beam runs along the top of the posts and there'll be a cross beam joining the main beam to the wall, so the cross beams are only 1 metre long. All green oak by the way.

Anyway thanks for the advice. - sounds simpler than I'd thought. Pity it's raining now otherwise I'd be out there finishing the main beam.

Cheers
Matt

 

[Penners]

Matt - as Middi says, your green oak will probably shrink by about 2.5% across the grain (in both planes) but shrinkage along the grain will be almost non-existent. So you really don't have much to worry about as regards the porch being pulled towards the wall.

Have you considered planting a sill on the wall and jointing the rafters (cross-beams) into it, as you are with sill on top of the posts?

 

[MattJ]

I will have a wall plate (is that a sill?, suppose so...) bolted onto the wall for the top of the minor rafters to sit on, but the structural engineer said the beams need to be in pockets as the principal rafters sit on uprights that are jointed into these beams and so the weight needs to be shared between the wall place and the cross beams (and he has more letters after his name than me - or at least more relevant letters).

Matt

 

[Penners]

he has more letters after his name than me

In which case I defer entirely to him!

Sill? Wall plate? I think the terms both refer to bearing members, so I'm not sure which is strictly correct here. In any event, as you undoubtedly gathered, I was using "sill" as shorthand for "a horizontal length of timber bolted to the face of the wall".

 

[David Dyer]

Probably more correct when fixed to the face of a wall would be ledger or ledger board.

 

[middi]

We are entering the realm of confusion as soon as we start discussing the various components which constitute the " house".

Be it a cave, a medieval house, a hovel or a skyscraper, they all have three common denominators. Entrance, walls and roofs.

The various materials and their definitions used to construct these type of dwellings are very specific to what goes where in their construction.

The confusion starts when one type of building is "intermingled" with another where lots of different materials are used, new terminologies are used and different metods of attaching one component to the other is employed.

The components of a cave is rock, the components of a timber house is post and beam, the components of a skyscraper in millions of bits and peces which architects gives different names .

Contemporary names of components for traditional buildings are frequently used, especially by contemporary architects, the irony is that unless some description is used nobody would know what the hell they are talking about. Even more ironical is the fact that after the description of a component there is no decription of it's purpose.

So, back to the wall plate.

What the heck is a wall plate, is it one which is hanging on the wall with princess diana's face on it, or is it a plank of wood nailed to the wall with coat hangers on it.

It could be a piece of wood where the rafters of a roof rest on and this piece of wood is resting on the wall, but then is this piece of wood which supports the rafters, but resting on posts, still be defined as wall plate.

Giving a " generally accepted" name to a component can be very mileading without concise description of its use.

Wall plate? where did it originate from as associated with the building industry and totally accepted as an important member of construction.

No wonder a lot of homes are poorly built

( sorry, just wondering)
.

 

[Penners]

Oh blimey, Middi. Now I'm even more confused!

 

[middi]

So am I.

 

[biffvernon]

I notice that the term 'ledger board' used to be used for the top rail of a fence or balustrade, but now its most common usage is in the realm of decking where it is, indeed, a piece of wood fixed to a wall to create a ledge on which the deck joists rests.

(Of course I don't know anything about decking.)

Ribbon board is the other term for desribing a horizontal timber that supports joist ends.