Attic Conversion - RSJs and Insulation

L

Lonan

Guest
Hi,

One of the contractors that gave me a quote said that unlike alot of 'cowboy' builders, he inserts the RSJ support beam slightly into the party wall aswell as the outside wall rather than 'just' bolting it on.

Another contractor told me this is illegal as you cannot interfere with the shared party wall. Anyone offer the correct regulation?

Also, one contractor said he would insulate the roof with 100mm Kingspan while another said that doesn't leave space for ventilation .. but I want to keep the attic room warm! Any advice on this also?

You really got to drill down with these guys.. all had glowing references!
 
You need to take professional advice before touching this building.
If your glowingly referenced builders build incorrectly you are wide open for a claim.
Structural interventions on party walls, compliance with Part F ventilation and correct insulation require competent persons to advise.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
 
Dont know in relation to RSJ.

On the insulation bit though - depends on the depth of the rafter. He has to leave a minimum of 50mm on the cold side of the insulation for ventilation. So it depends on your rafter depth.
 
CBGB said:
He has to leave a minimum of 50mm on the cold side of the insulation for ventilation. So it depends on your rafter depth.
Click to expand...

Not necessarily. That only applies if the roofing felt is sarking felt, i.e. non-breathable bitumous type. If it is the newer breathable type membrane, then this will not apply.
 
@Shane007.

You might think so, but AFAIK the prima fascia compliance/approved details show the 50mm air gap.
With no gap, you are relying solely on the integrity of the material remaining vapour permeable over time.
It will transpire 15 Litre of water vapour per day into a space that is not well ventilated, which causes concern.
But if it is a continuous membrane and it fails over time, you are sealing the water vapour in the structural sandwich.
AFAICR, there are no empirical studies proving that these new "sealed" details work in Ireland except over the short term.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand
 
Hi ONQ,

If you check with Environ.ie, Acceptable Construction Detail http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,18751,en.pdf you will see from page 17, this form of detail is acceptable.
 
(chuckle)

Silly drawings dealing with insulation and sealing
I ralied about these naive documents at Plan Expo 2009.
Look at sheet ten, the block wall inner meeting the masonry outer.
How are you meant to carry the vapour check through the masonry bonding?
I rely on my competence and experience, and not those details, many of which are not well considered.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand
 
Some manufacturers may beg to differ.

My point is that the OP states an argument/difference of opinion regarding the ventilation space at that point and as we may differ, it does not infer that the builder in question is a "cowboy".

ACD's clearly state this is an acceptable form of construction and if there is indeed installed a breathable membrane, then I am afraid the builder who stated this fact is correct. Now whether he has gone to the trouble of seeking further material specification and limitations of said material is another matter and whether 100mm of polyiso or phenolic will satisfy the required U value remains to be seen.
 

You will need to take some structural engineer's advice on this one.

Here's my two-pence worth.

What is the construction of the party wall?

What is the thickness of the party wall?

Are you converting an attic, give some additional background information please.

I have highlighted the two most dangerous words above. If you put the beam slightly on the party wall is there a slight chance that it could fall off?

If you just bolt it onto the wall, the RSJ may not fail, nor the bolts, but there just could be a compressive load failure in the party wall (soft bricks etc.)

Normally you could bear half way onto the party wall, ie your side, and put in a concrete bearing pad to spread the load, however this is a forum only & my engineering advice should be only taken with a grain of salt.

I think the second contractor is on about, lets say you use the full bearing width of the wall, then there very well will be a fire spread issue to your adjoining neighbour's house.
 
On insulation I would always insist on a 50mm clear airspace on the cold side of the insulation (between the top of the insulation and the underside of the roofing felt) whether or not the roofing felt is breathable.

In addition, I would insist on the provision of the eqivalent of 25mm continuous strip ventilation at eaves and equivalent of 5mm continuous strip ventilation at the ridge.

For existing houses this usually means adding vents at the eaves and taking off all the ridge tiles and re-fitting with a proprietary ventilation system (such as rediroll). I have yet to come across an attic conversion company that does this.
 
Docarch said:
For existing houses this usually means adding vents at the eaves and taking off all the ridge tiles and re-fitting with a proprietary ventilation system (such as rediroll). I have yet to come across an attic conversion company that does this.
Click to expand...

You mean they'd have to employ someone who actually has a trade [like a roofer], instead of the usual shower of handymen and third year apprentices masquearading as carpeters, electricians and plumbers that go around with them? Perish the thought. LOL!

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
 
OP - as stated above, you need to speak to a structural engineer regarding the RSJ for your specific project.
I recently completed an attic conversion - terrace house - we had to cast concrete padstones or bearing pads into the party walls with the steel beams then resting onto these pads. I queried weather we could bolt onto the party walls but our Engineer would not allow this - apparently the issue with this is the connection between the bolt and the block; it's not a question of the bolts not being strong enough but rather getting a suitable connection between the bolt and the block
 
+1 what oraa has posted.

The beam is something that generates a point load on a block wall without reinforcing piers.
If the bearing wall is hollow blockwork you could be getting a point load of several tonnes bearing on the thin wall of a hollow block - 25mm/1 inch of concrete.
The minimum bearing is six inches /150mm of bloclwork by the Part A rule of thumb, but this depends on the load and type pf wall and thickness and you may in fact need a pier.

Even if the block is solid blockwork there is a risk it may crush the block or cause local cracking.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
 
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