Hole for gaine in floor beam

[JohnRoss]

Is there any reason, (regs or something else) why I should not drill a hole in a wooden beam supporting a floor and pass flexible electrical conduit (gaine) through. The beam will not be significantly weakened by this. Thanks in anticipation..........................JR

[pachapapa]

Depends on the size of the hole for the gaine in relation to the depth of the beam. personally I would drill it close to the wall and just above the neutral axis.

[JohnRoss]

Thanks and the hole will be close to the wall, 4.5 cms from it, and my concern was if there were French regs from an electrical safety point of view. The beam is 19 x 8 cms with the longest dimension vertical as you might expect. The hole will be 18mm.......JR

[master of none]

Some info. here from a UK local authority building dept. which may be of help.  I realise it's not French reg's but should offer some guidence.  Don't know why the images are not visible but you get the idea!

 

Beams, rafters, purlins and binders must never be notched or drilled

without calculations

to justify the remaining timber.

Rafters may be birdsmouthed by no more than 1/3rd of the depth.

If joists are more than 250mm deep, seek structural advice.

Remember

Before you start work check that the joist size is adequate - see below

Notches may only be made in the top of the joists, within the permitted

area.

Holes may only be made on the joists centreline within the permitted

area.

Please phone if you need further advice

Safe areas for

notching

Depth and position of notches must be within the zones shown in this

diagram and only

in the top of the joists.

 

Notches of other sizes or in other locations

may be acceptable if the joist is sufficiently

oversized

 

Example to calculate safe areas

Measure the clear span between supports and joist height .E.g. 3.0m

(10’0”) and 150mm

(6”).

Figures in bold type are constants

Safe area for notching is between ....

0.07 x 3.0 (10’0”) = 210mm (81/2”)

and

0.25 x 3.0 (10’0”) = 750mm (30”)

The maximum depth of notch is ....

0.125 x 150mm (6”) = 19mm (3/4”)

So, safe areas to notch are from 210 to 750mm from either wall, and up

to 19mm deep.

 

 

Safe areas for

drilling

Size and position of holes must be within the zones shown in the diagram

overleaf and

only on the centre line.

Adjacent holes must be at least twice their diameter apart and no hole

may be within

100mm (4”) of a notch.

Example to calculate safe areas

Measure the clear span between supports and the joist height.

E.g. 3.0 m (10’0”) and 150mm (6”).

Figures in bold type are constants.

Safe area for drilling lies between ....

0.25 x 3.0 (10’0”) = 750mm (30”) and

0.40 x 3.0 (10’0”) = 1200mm (48”)

The maximum diameter of hole is ....

0.25 x 150mm (6”) = 38mm (11/2”)

So safe areas to drill are from 750

to 1200mm from either wall, and up to 19mm deep.

 

 

Safe areas for

drilling

Size and position of holes must be within the zones shown in the diagram

overleaf and

only on the centre line.

Adjacent holes must be at least twice their diameter apart and no hole

may be within

100mm (4”) of a notch.

Example to calculate safe areas

Measure the clear span between supports and the joist height.

E.g. 3.0 m (10’0”) and 150mm (6”).

Figures in bold type are constants.

Safe area for drilling lies between ....

0.25 x 3.0 (10’0”) = 750mm (30”) and

0.40 x 3.0 (10’0”) = 1200mm (48”)

The maximum diameter of hole is ....

0.25 x 150mm (6”) = 38mm (11/2”)

So safe areas to drill are from 750 to 1200mm from either end and up to

38mm

diameter.

 

 

 

 

 

 

 

[JohnRoss]

Many thanks for this useful information which I have copied to keep for future reference. I have found since posting that I can run the gaine under the beams in the inter-wall space so no need to drill now but from your info it looks as though my proposed 18mm hole near the wall end of the beam would not significantly weaken the structure anyway, thanks again.............JR.

[pachapapa]

Even with the diagrams it seems daft.

It must have been written by a jobsworth with a peaked  hat and a yellow band round it, whilst on light duties after inadvertently stubbing his toe on a parking meter.

http://www.broxbourne.gov.uk/environment_and_planning/building_control/notching_of_joists.aspx

[master of none]

Glad you found it useful pachapapa!

[pachapapa]

[quote user="master of none"]Glad you found it useful pachapapa![/quote]

I love this piccy:

[IMG]http://www.broxbourne.gov.uk/images/drilling_v_Variation_1.jpg[/IMG]

There may in fact be a plausible argument for the 0.25-0.4 distance from the buttress for an encastré RSJ when there will theoretically be a point of inflexion in the neutral axis at approximately 1/3 of the half span from each end of the beam.

However this will in no way reflect the situation with a simple uniformly loaded timber beam supported by a traditional stone, lime and rubble wall. The wall will accomodate the deflection of the beam at both ends resulting in a beam with no inflexion points on the neutral axis and simply an upper portion in compression and a lower portion below the neutral axis being in tension.

In principle wood is stronger in compression than in tension and accordingly any hole drilled through the beam should be in the upper portion and certainly not nearer than 3x the hole diameter from the top of the beam.[:P]