Extra beams in attic - summil beams?

[Mike400]

I dont have any pictures at the minute so bear with me!

The joists that make up my attic floor run from the front of the house to the rear.

There are three beams on top which run at right angles to the joists, from the gable wall to the party wall. They dont quite touch the two walls and dont appear to be fixed to anything (I havent looked too closely yet)

The cold water tank sits in the middle of the attic, on top of the middle beam.

I would like to convert the attic at some point, and would need to removed the one in the middle (the other two are out of the way)

I was going to double up on the joists anyway I was just wondering what these beams are there for?

Ill try and get some pics up later

 

[noseall]

they are ceiling binders, or as you say summil beams.

they are there to stiffen the ceiling joists, without them there would be excessive 'whip' in the ceiling.

they would be built into the walls these days and be rather large too.

what size are the existing ceiling joists?

 

[Mike400]

Not sure to be honest, ill measure them when I get the chance to take some pics.

These summil beams look to be the same size as the joists.

 

[noseall]

how old is the house?

 

[Mike400]

I think the house was built in the 1950's, at least thats what the next door neighbours say and they moved in to theirs when it was built!

Its a semi, of concrete block construction (brick facing to front elevation).

As well as these beams there are also two inverted 'V' shapes in the middle of the attic I want to remove also.

I should get a chance to take some pictures later on.

 

[Shytalkz]

As well as these beams there are also two inverted 'V' shapes in the middle of the attic I want to remove also.

They'll be purlin props then. Don't go taking them out, without the purlin either being strengthened, or rendered redundant by picking the roof slopes in some other fashion.

 

[Mike400]

Cheers guys.

What I thought I could do was double up on the joists, then double up on the purlins as well as "boxing in" the space im going to use with beams going vertically from the joists to the purlins.

Once thats done I thought I could safely remove the purlin props and the summil beams....

Either way ill get some pics up

 

[Mike400]

Ok not a picture but should give some idea:



The red bits are the summil beams, the green the purlin props.

There are only two sets of props

 

[Shytalkz]

They'll be purlin props then.

Ignore me, I missed the keyword "inverted"...!

Not sure what purpose they actually serve, are you not missing a further one either side that goes back up to the rafters?

 

[Mike400]

They'll be purlin props then.

Ignore me, I missed the keyword "inverted"...!

Not sure what purpose they actually serve, are you not missing a further one either side that goes back up to the rafters?

AFAIK thats as far as they go. Ill get a chance later or tomorrow to get up and take some pics, that would probably tell more than my crappy drawing lol

They dont seem all that substantial, which is why I thought a bit of bracing from the joists to the rafters would more than compensate for removing them.

 

[noseall]

"doubling up" the joists with joists the same size will not be enough. you will need to fit something considerably deeper in order to achieve a 'habitable' floor.

once installed and the floor covering fitted, there will be no need for ceiling binders.

if the loft is to be used as storage then joists at 90 degrees to existing will account for loading and allow the extra space needed for loft quilt insulation.

 

[Mike400]

"doubling up" the joists with joists the same size will not be enough. you will need to fit something considerably deeper in order to achieve a 'habitable' floor.

once installed and the floor covering fitted, there will be no need for ceiling binders.

if the loft is to be used as storage then joists at 90 degrees to existing will account for loading and allow the extra space needed for loft quilt insulation.

sorry still no pics yet!!!

I had heard you can double up on the existing joists using beams which arent any higher but are wider, thus giving the same strength as a taller joist?

The finished room would be used as a study and so wouldnt be used as heavily as say a bedroom would.

 

[noseall]

I had heard you can double up on the existing joists using beams which arent any higher but are wider, thus giving the same strength as a taller joist?

the laws of physics do not work this way i'm afraid.
depth of joist is paramount and can not be substituted in width by the same increment.

the ratio will increase at an alarming rate.

a 2" wide joist at 10" deep is a LOT stronger than a 10" wide joist at 2" deep.

 

[Shytalkz]

Ah, but is a 100x100 stronger than a 50x150...? [No, as it happens! But it is stronger than a 50x125 ].

The reason that height has the greatest effect is because the timber stresses are a function of the square of the height and deflection is a function of the cube of the height.

 

[Shytalkz]

The finished room would be used as a study and so wouldnt be used as heavily as say a bedroom would.

doesn't matter: floors in domestic situations have to be designed for a live load of 1.5kN/m2, regardless of room use/designation.