Running lighting circuits in the loft space.

[chris murphy]

I've always wondered how those joists manage to carry all that new insulation they stick up there nowadays :carolers:

"Hello Amp David",


You might remember [as You replied to Me] that I enquired about Electrical Cables being affected by Loft Insulation prior to one of My Relatives having their Loft Insulated with 270 mm of Fibre Glass Blanket Insulation.

The Loft has been Insulated now and My Relative is disappointed with how much the Loft Space has been `diminished` in relation to what they had thought would be `Left`.

They thought that they would be able to just Lay Down some Boards on top of the Loft Insulation wherever they liked and put items onto those Boards - Until I told them that it is the Thickness / Air Space within the Thickness of the Fibre Glass Blanket Insulation that actually forms the Insulating `Barrier` - and that `Flattening` the Insulation would negate the Full effectiveness of the Insulation.

I told them to actually Insulate the area where they wanted to board for storage [Small Amount of 100 mm Blanket Insulation between Ceiling Joists ] - Board it out - and that the Loft Insulators would then Overlay the 170 mm `Top Layer` onto the Boards which My Relatives could then move to Store items - When they wanted to do so.

They did the 100 mm Insulation between the Ceiling Joists and used Loft Boards to Board an area in the Loft Space.

The Loft Insulators refused to Overlay the Boarding - Until My Relative telephoned Me and asked them to explain the reason to Me - When I explained My Profession and My Knowledge of Heat Loss / Insulation to them and told them that there was NO Reason to Refuse to Overlay the Boarding - they then reluctantly agreed to Overlay the Boarding.


I had mentioned the Difficulties of accessing areas of the Loft Space AFTER the Loft Insulation - but People don`t realise exactly HOW Difficult / Dangerous this can be until they actually SEE what the Loft looks like after it has been Insulated.


Regards,

Chris

 

[ackbarthestar]

I think there are other ways of insulating loft spaces and saving lots of space, such as the use of solid 'foam' cut to fit between the rafters and then covered with aluminum 'bubble wrap'

 

[chris murphy]

I think there are other ways of insulating loft spaces and saving lots of space, such as the use of solid 'foam' cut to fit between the rafters and then covered with aluminum 'bubble wrap'

"Hello ackbarthestar",


I think that We discussed this in the other Thread where I went into a LOT of detail about Loft Insulation:


If you `Insulate` between the Rafters as You describe in your Post - Unless the Loft is going to be Converted into Living Space the Temperature of the Loft would still be Very Cold regarding the Ventilation / Advantitious Ventilation.

The Ventilation - either purpose provided OR Accidental / Adventitious means that the AIR in the Loft Space would be almost as Cold as the Outside Temperature - You would still be Losing the Heat from your Rooms into the Loft Area - Because of the Insulation in the Rafters you would now be Heating the Loft Area with the `Heat Loss` from the Home.

Regards,

Chris

 

[ackbarthestar]

Good point about ventilation, however, this method can also be applied between the loft joists and then boarded over if necessary.

 

[chris murphy]

Good point about ventilation, however, this method can also be applied between the loft joists and then boarded over if necessary.

"Hello Again ackbarthestar",

Good Idea - But I believe that this Sheet Type Insulation is VASTLY Expensive - I would hate to think how much it would Cost - even for My Loft Space which is approx. 100 SQ. Metres - ?

I have also been told that the Sheets are NOT the Ideal Width for putting between the Rafters OR Joists - meaning a LOT of Off Cuts - On VERY Expensive Sheet Insulation !

Obviously If the Cost was Not a problem this type of Loft Insulation would probably be the BEST regarding what You mentioned about Boarding Over the Joists - The required Insulation Rating within an approximately 100 mm Joist Depth.



"Happy Christmas and New Year" to You.


Chris

 

[ackbarthestar]

"Hello Again ackbarthestar",

Good Idea - But I believe that this Sheet Type Insulation is VASTLY Expensive - I would hate to think how much it would Cost - even for My Loft Space which is approx. 100 SQ. Metres - ?

I have also been told that the Sheets are NOT the Ideal Width for putting between the Rafters OR Joists - meaning a LOT of Off Cuts - On VERY Expensive Sheet Insulation !

Obviously If the Cost was Not a problem this type of Loft Insulation would probably be the BEST regarding what You mentioned about Boarding Over the Joists - The required Insulation Rating within an approximately 100 mm Joist Depth.



"Happy Christmas and New Year" to You.


Chris

Its about £60 per roll and 1 - 2 rolls with sealing tape will cover more of less any reasonably sized loft space... Its also good for space explorers !

 

[41steve]

soz, i was on about electrics for a loft conversion. i ment to say trusses an not joists!

 

[chris murphy]

Its about £60 per roll and 1 - 2 rolls with sealing tape will cover more of less any reasonably sized loft space... Its also good for space explorers !

"Hello ackbarthestar",

I am a bit confused now - when You mentioned the `Solid Foam` Insulation in this comment:

`I think there are other ways of insulating loft spaces and saving lots of space, such as the use of solid 'foam' cut to fit between the rafters and then covered with aluminum 'bubble wrap'



I thought that You meant the SHEETS of Foam Insulation - Perhaps sold in sizes something like 1200 mm X 600 mm X 50 mm - Foil Sheet applied to both sides.

It was this type of Sheet Insulation that I meant was VERY Expensive.


Chris

 

[robsparky1975]

soild foam,is it celotex you mean?

 

[Mr.Si]

soild foam,is it celotex you mean?

That is what I thought it meant too.

Sent from my Samsung Galaxy S II via Tapatalk

 

[chris murphy]

soild foam,is it celotex you mean?

"Hello robsparky 1975",


I was thinking of Kingspan Insulation - But I think that Celotex is a very similar product although I have never compared the Specifications of the 2 products.


Chris

 

[ample current]

Where is a good place to run cables in a loft space so they dont get buried in 300mm of insulation?, is it better to run them on the plaster board or clip to the lower edge of the ceiling joist or the top edge of the ceiling joist or lay over the insulation or use 300 miles of cable to right round the edges to go from the light fitting to the switch, at some point u surely have to go over the joists where they mayby troden on.

Cheers Mark

 

[ackbarthestar]

Where is a good place to run cables in a loft space so they dont get buried in 300mm of insulation?, is it better to run them on the plaster board or clip to the lower edge of the ceiling joist or the top edge of the ceiling joist or lay over the insulation or use 300 miles of cable to right round the edges to go from the light fitting to the switch, at some point u surely have to go over the joists where they mayby troden on.

Cheers Mark

IMO, the only place where cables run over the joists is where they unlikely to get in the way, such as tucked into the eaves, and always clipped to the side of the joists.
I used to know a chap who worked for a national building services company who never specified any lighting conductor size less than 1.5mm2 ........

 

[Mr.Si]

Sorry to dig this out again folks, but I went to the b&q place today to buy some loft panels.

Thought i would post what SOME of the instructions say:

1. You must re-route any cables that cross joists. Drill a hole on the centre line of the joist large enough for one cable. If more than one cable is involved, drill another hole on the centre line at least 50mm from the first.

Other instructions prior to this are to isolate any of the circuits which may be involved in the loft space.

Thought it may be good to post info about what Joe public are given as advice by manufacturers.

Sent from my Samsung Galaxy S II via Tapatalk

 

[ackbarthestar]

Sorry to dig this out again folks, but I went to the b&q place today to buy some loft panels.

Thought i would post what SOME of the instructions say:

1. You must re-route any cables that cross joists. Drill a hole on the centre line of the joist large enough for one cable. If more than one cable is involved, drill another hole on the centre line at least 50mm from the first.

Other instructions prior to this are to isolate any of the circuits which may be involved in the loft space.

Thought it may be good to post info about what Joe public are given as advice by manufacturers.

Sent from my Samsung Galaxy S II via Tapatalk

I suppose that's fine for the part time 'electrician' , probably quicker to hack the offending joist out of the way completely, then there's no problem of running it over the top

There must be a good read out there, somewhere such as, 'Thomas' electrical wiring schedules for tank engines'

 

[chris murphy]

Sorry to dig this out again folks, but I went to the b&q place today to buy some loft panels.

Thought i would post what SOME of the instructions say:

1. You must re-route any cables that cross joists. Drill a hole on the centre line of the joist large enough for one cable. If more than one cable is involved, drill another hole on the centre line at least 50mm from the first.

Other instructions prior to this are to isolate any of the circuits which may be involved in the loft space.

Thought it may be good to post info about what Joe public are given as advice by manufacturers.

Sent from my Samsung Galaxy S II via Tapatalk

"Hello Mr.Si",


What You quoted in your Post shows how Unreliable the `Instructions` from these Companies can be !

Apart from it NOT being the Correct thing to do - Drilling Holes in what are usually less than 100mm Deep Ceiling Joists - Even IF the Ceiling Joists were of a Bigger Size - there are Zones within which Joists are supposed to be Drilled - without the `Instructions` stating those Zones there should be NO mention of Drilling the Ceiling Joists.

Imagine Joe Public deciding to alter the Run of the cables in the Loft Space - as most Lights are in a central position in rooms - it would possibly follow that He would Drill holes in the Ceiling Joists across the Centre of the Joist span for each Room - If perceived to be the `Shortest Route` !

Obviously when re-routing cables it would sometimes be necessary to replace lengths of cable with longer ones to do this - some People would be prepared to do that - But I am fairly sure that if We asked someone who did not have any experience of the Electrical / Plumbing / Building Industries WHERE They would Drill the Ceiling Joists to run cables to Room Lights - Most of these People would be taking the Central [of the Room / Joist Span] Route !

Although Drilling the Ceiling Joists might not affect the `Holding` of the Ceiling - as mentioned previously If part of the Roof Structure this would be an Immediate Breach of the Building Regulations - and If in a Terraced Property this could affect more than the Property Roof where the Structure was compromised !


Chris

 

[Mr.Si]

Conti, the Manufacturer in this case and all other manufacturers need to have a rethink and get the install instructions changed to say "contact an electrician to reroute cables for you" maybe.

Sent from my Samsung Galaxy S II via Tapatalk

 

[ackbarthestar]

"Hello Mr.Si",


What You quoted in your Post shows how Unreliable the `Instructions` from these Companies can be !

Apart from it NOT being the Correct thing to do - Drilling Holes in what are usually less than 100mm Deep Ceiling Joists - Even IF the Ceiling Joists were of a Bigger Size - there are Zones within which Joists are supposed to be Drilled - without the `Instructions` stating those Zones there should be NO mention of Drilling the Ceiling Joists.

Imagine Joe Public deciding to alter the Run of the cables in the Loft Space - as most Lights are in a central position in rooms - it would possibly follow that He would Drill holes in the Ceiling Joists across the Centre of the Joist span for each Room - If perceived to be the `Shortest Route` !

Obviously when re-routing cables it would sometimes be necessary to replace lengths of cable with longer ones to do this - some People would be prepared to do that - But I am fairly sure that if We asked someone who did not have any experience of the Electrical / Plumbing / Building Industries WHERE They would Drill the Ceiling Joists to run cables to Room Lights - Most of these People would be taking the Central [of the Room / Joist Span] Route !

Although Drilling the Ceiling Joists might not affect the `Holding` of the Ceiling - as mentioned previously If part of the Roof Structure this would be an Immediate Breach of the Building Regulations - and If in a Terraced Property this could affect more than the Property Roof where the Structure was compromised !


Chris

Or as 133.1.3 states in BS7671

 

[chris murphy]

Or as 133.1.3 states in BS7671

"Hello ackbarthestar",


I think that I mentioned to one of the other Members in a previous Post that as I am NOT an Electrician and I do not carry out Electrical Work associated with My Heating Systems - even though I have completed the Defined Scope Electrical Part P Course and Assessment - I do not have a Copy of BS7671 `To Hand`.

I do have various Electrical Books - including the IEE [as was] On Site Guide - But that is not `Findable` at the moment.

Is there a reference in the Regulation / Reference that You quoted that you could put into words - a relevant Paragraph perhaps - ?

I would be interested in what You were quoting IF it is not Too Detailed to refer to - ?


Regards,


Chris

 

[ackbarthestar]

"Hello ackbarthestar",


I think that I mentioned to one of the other Members in a previous Post that as I am NOT an Electrician and I do not carry out Electrical Work associated with My Heating Systems - even though I have completed the Defined Scope Electrical Part P Course and Assessment - I do not have a Copy of BS7671 `To Hand`.

I do have various Electrical Books - including the IEE [as was] On Site Guide - But that is not `Findable` at the moment.

Is there a reference in the Regulation / Reference that You quoted that you could put into words - a relevant Paragraph perhaps - ?

I would be interested in what You were quoting IF it is not Too Detailed to refer to - ?


Regards,


Chris

133.1.3 read in conjunction with 134.1.1 briefly states that work done and equipment used outside of its standard needs to be assessed for risk by a competent person (all my words )