Bouncing loft floor

[Rob]

Hello all.
After receiving some extremely useful replies to my previous posts I thought I would try to tap into your collective experiences and knowledge regarding my loft floor.
My house is a large stone built property over 300 years old. The loft has been converted and boarded previously, but over time has sagged and become a little "bouncy". I believe it was the grain store as the house was previously a bakehouse.
With a new offspring on the way we need to use this as a bedroom and I am endeavouring to tackle the lack of insulation and uneven floor.
The room is approximately 6 m long and 5m wide. The joists currently run side to side spanning a central oak beam, overlapping in the middle. This means each beam goes approx 2.5m from the centralbeam to the wall.
Unfortunately they do no sit directly on the wall plate, but are screwed/bolted/tennoned into what appears to be old small "branches" approx 2 inches thick going down at an angle to the wall plate (i hope this makes sense)
The rafter are approx 4x2 thick and are all at the most 12 inches apart. I am thinking of screwing thin pieces of wood to the top of each rafter and laying flooring over the top to level it up.
My questions are:
Will this be strong enough to use as a bedroom?
Will the flooring help the overall stiffness?
Should i add additional noggins between the joists?
Any other ideas?

Any advise or experiences of a similar nature would be most appreciated.
Rob.

 

[NT]

If the wood is in decent condition, screw&glue-ing 2x2 or 3x2 onto the top of the 4x2s would make all the difference.

http://wiki.diyfaq.org.uk/index.php?title=Strengthen_a_Wood_Floor

NT

 

[chuckey]

The oak beam, is it OK?, because if that is springy this will have to be rectified first.

The 4 X 2s are laid 4" upwards? So they have a little extension going into the wall?. this looks to me as thought the ceiling has been raised at some time. As built the ceiling would have been underneath the oak beam, at some time they decided to raise the ceiling over the oak beam, then discovered that eaves were too low.

4 X 2 are too small for floor joists, I would see my local metal worker and have him fabricate up brackets out of 3mm mild steel like joist hangers but going upwards and cement these onto the walls to carry new 6 X 2s in between the existing joists. The centre of the 6 X 2s can be blocked up on the oak beam to set their levels so there is a small clearance between the bottom of the new joists and the top of the plastered ceiling.

Using noggins on 4 X 2s will not increase their stiffness, due to the limited height(4").

Another alternative could be to plate the joists, BUT the plates would have to have ends welded on them so they extend over the "brackets?"

Out of curiosity, the deflection on a beam is proportionel to its length (2 X long = 2 X droop). The deflection of a beam is proportionel to the depth of it cubed ( 2 X deeper= droop X 1/8)
Frank

 

[chuckey]

Hi NT, Wiki got it wrong!!!! You are correct, BUT you must use a structural* adhesive and use screws that go right through to at least 2 " into the old joist and at least 1 per 9". It will be difficult to get a really good fit between the two bits of wood. The brackets at the ends, are a BIG problem with this method. I suppose the the joists can be backed up and then the brackets have 1" ply glued/screwed to them going right over the faces of the "new" joists.
Frank
* not PVA

 

[NT]

How are the end brackets an issue with this approach? Unless I'm mistaken, 4x2 has plenty enough strength for the additional timber to just stop short of any end hangers.

What type of glue would you recommend?


NT

 

[Rob]

hi guys.

cheers for the responses.
It is interesting to hear you say you think the ceiling rafters may have been moved from below the central beam to above it. The house is over 200 years old and was an old bakehouse. There is still remnants of wood sticking out of the wall above the attic window where i believe they used to whinch the floor into the attic? The house was originally thatched and the wood the joists are secured to are similar is size and style to the others so i believe there were the original roof rafters that have been cut short when the slate roof was fitted.
As the only concrete walls i can fix new rafters to are 6m apart, I am reluctant to fit new joists into these due to the depth of joist needed to span that distance with no supporting wall.
Also I cant fix batterns above the exisiting joists as they are laid side by side on the central beam and therefore not in line accross there length.
Any other ideas?

 

[MdB]

... they used to whinch the floor into the attic ...

Clever our ancestors, weren't they.

Any chance of some pictures to show us what is going on?

 

[Rob]

Hello.
Hopefully you will see a photo with this.
The floor joists are the straight ones along the bottom, the roof rafters the ones going up at an angle.
As you can see the floor joists are secured into old and broken off bits of wood that I believe were the structure of the thatched roof

Hope this helps

Rob



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[Nemesis]

I think you might have Building Regs difficulties to consider...

 

[Rob]

I have discussed this with the authorities and they have informed me that due to the fact the conversion was done so long ago they do not need to confirm to current building regs. As the house sits there are no bulding regs issues and all i wish to do is to remove some of the "bounce" from the floor by adding some additional supports and would like peoples advice as to the best way to go.

Rob.

 

[Nemesis]

Do they regard this as a usable room now?

Hmmm.

How is it accessed?

 

[Rob]

hello.
yes this classes as a usable room and so is the room next to it even without any windows!
This level is accessed by a staircase from the first floor landing. As i said the main part of the house is over 300 years old and these rooms were built with the house therefore are not going to comply.
When i moved in the floor was nicely carpeted and the roof rafters plasterboarded. I have now removed the plasterboard as it was bolted direct onto the rafters with no insulation at all. I am planning to add some of the "tri iso" type insulation between the rafters. ( dont shoot me!)

 

[MdB]

Do they regard this as a usable room now?

Hmmm.

How is it accessed?

And how do you get out of it in an emergency? You can't convert a loft into a bedroom just by adding a bed. Building control and possibly planning will have to be involved.

I think you also need to get a structural engineer involved to work out what is required in strengthening work.

 

[Nemesis]

Are you intending to put in windows?

If so I suspect BR may come into it.


Tri-iso... hmmmm.

Nothing to prevent it being used as a bedroom, of course, but selling it one and describing it as such might prove a problem.

 

[Rob]

ok. here goes.
I purchased the house as a 2 bed repossession. I called the building inspector out and asked him i could class these two attic rooms as bedrooms.
He looked at them and declared that even though we do not have self closing fire doors, escape windows, electric smoke alarms etc, because the rooms have been bedrooms for so long (a 90 year old granny round the corner married the guy who grew up in one) they can be classed as bedrooms. all i am planning to do is to add a little insulation to the roof and take some of the bounce out of the floor.
any ideas?

 

[NT]

Since all the OP is doing is strngthening the floor in an already habitable room, I think its correct to say no BRs apply.

I'm not clear why no noggins would be fittable though. These would reduce flexing due to point loads and reduce creaking and cracking.


NT

 

[Nemesis]

Odd - people have posted here in the past to say thay have had problems with similar situations.

I suppose if you aren't adding anything such as windows no regs come into it.

 

[Rob]

I am considering adding a velux type window in above the stairs to add light to the room and stairwell, but this will be on the landing and outside of the bedroom. I am waiting to here back from the planning commitee on that one as we are in a conservation area.
If i list my plans could people please give me their thoughts?

-Lift old worn and soft floorboards
-bolt rafters together where they cross central beam
-add some noggins between rafters
-use metal straps to add support to ends of rafters up to 12" thick beam running approx 8 inches above the ends of the rafters
-screw 4 sided T&G flooring accross all rafters

would this help the bounce or should i just accept it?
many thanks for your help so far

Rob

 

[Nemesis]

Please don't fit one of those modern plant on punched through Velux lights - unless it's a conservation type...

 

[chuckey]

Rob can you confirm that there is no "bounce" in the centre of the room, which will confirm the state of the Oak beam because the 4 X 2s are resting on it.

Bolting the 4 X 2s together across the top of the oak beam will only marginally increase their stiffness (few %) if the beam is OK, BUT, if one or another moves sideways as the bolts are tightened, it will possiblely wreck the plaster ceiling. I would advise against this unless the joists are are really good fit (gap less then 1mm) especially around where the bolts are going to tighten. if the gap is larger, it will need to be packed out with some shimming material. If the material is coated with urathane glue, it might help as it expands slightly on setting. Use 2" square steel washers under the nut and the bolthead.

The idea of backing up the joists could be done by using a 4 X 2 laying down so 1/2 of it is over each joist. Height = X 1.5 deflection goes down by 3.375.
Frank