Need help with interpretation of Part L for an Extension

icbarros

Hi,

I would appreciate if you could help with the following.

When applying Part L, Paragraph 2.1.2.4 to an extension to an existing dwelling house, the relevant floor area may be taken from:
(a) whole house method
or
(b) extension alone

1 - Let's say I use method (a) whole house, and I get U-value=1.31.
Is this U-value to be used in my NEW windows/doors (only) or in the ALL house?

I'm lead to think this should be for the ALL house since it's an Average U-value. If I follow this way of thinking I would either have to replace the existing windows (to have the all house with 1.31) or have an U-value of 0.39 for the new ones, which is not possible.

What are your views on this? Maybe I am not interpreting this correctly and the 1.31 value is just for the NEW windows, and the existing ones can be maintained with whatever U-value they have...??

2 - If using method (b) extension alone, can anyone explain what the last sentence of 2.1.2.5 (b) means:

"In this case, the maximum combined area of external doors, windows and rooflights derived using Table 6 can be increased by an area equivalent to the area of external door; window and rooflight openings of the existing dwellings which have been closed or covered over by the extension."

An example would make things more clear to me...

Thanks in advance for your comments.

Mellor

icbarros wrote: »

Hi,

I would appreciate if you could help with the following.

When applying Part L, Paragraph 2.1.2.4 to an extension to an existing dwelling house, the relevant floor area may be taken from:
(a) whole house method
or
(b) extension alone

1 - Let's say I use method (a) whole house, and I get U-value=1.31.
Is this U-value to be used in my NEW windows/doors (only) or in the ALL house?

I'm lead to think this should be for the ALL house since it's an Average U-value. If I follow this way of thinking I would either have to replace the existing windows (to have the all house with 1.31) or have an U-value of 0.39 for the new ones, which is not possible.

What are your views on this? Maybe I am not interpreting this correctly and the 1.31 value is just for the NEW windows, and the existing ones can be maintained with whatever U-value they have...??

If using method a.
You use the area of new windows, plus existing windows (less any made redundant) as a % of the combined area. This gives you a u-value to apply to the new windows.
Basically they can't force you to retro fit new windows, or improve existing.

Consider it like this, the lower the glazed area of the existing house, the more leeway you are entitled to with new windows. Which makes sense, right?

2 - If using method (b) extension alone, can anyone explain what the last sentence of 2.1.2.5 (b) means:

"In this case, the maximum combined area of external doors, windows and rooflights derived using Table 6 can be increased by an area equivalent to the area of external door; window and rooflight openings of the existing dwellings which have been closed or covered over by the extension."

An example would make things more clear to me...

Thanks in advance for your comments.

This means that you can offset existing windows made redundant against new windows.

Example;
Extension A - Built off a gable wall with no windows
With u-values of 2.0, the max area of openings is 25%
with u-values of 1.7, the max opening is 30.2%

From Table 6; or Aope/Af = 0.4325/(Uope - 0.27).


Ok, so that's a bog standard situation. But, now say we build off the read wall and we enclose, or demolish a window and door with total are of 4sq.m.

Now;
With u-values of 2.0, the max area of openings is 25% + 4sq.m
with u-values of 1.7, the max opening is 30.2% + 4sq.m


You can work it both ways, either;
- if know the area, minus the area of enclosed windows and work out the u-value reuired
- If you know the average u-value you'll achieve, work out the area and add on area of enclosed windows to get the new max area.

THe reason for this increased max is that you are essentially improving a section of old windows (as the new max requires new windows) and this extension actually proforms better than that in example A.

icbarros

Thanks very much for the answers Mellor.
They are quite helpful, but are you 100% sure about this?

Mellor wrote: »

This gives you a u-value to apply to the new windows.

It makes sense, alright. But we have had a few discussions in the office about this and in the last similar situation our BER assessor was of the opinion the average U-value had to be for the ALL house (in opposition to NEW windows only). Because of this we had to suggest to the client to replace all windows in order to have about 1.4 in the all house (or the alternative would have been a passive house standard window 0.65 or so for the extension).

Is everybody else of the opinion that the average u-value is to apply to NEW windows only?

Mellor wrote: »

- if know the area, minus the area of enclosed windows and work out the u-value reuired.

That would be the way I would normally work and I can see now why this was confusing to me. I actually have to subtract the area :rolleyes:, instead of increasing.
Things are much clearer now. Thanks again.

Mellor

icbarros wrote: »

Thanks very much for the answers Mellor.
They are quite helpful, but are you 100% sure about this?

Quite sure. Building regulations apply to new works only.

It makes sense, alright. But we have had a few discussions in the office about this and in the last similar situation our BER assessor was of the opinion the average U-value had to be for the ALL house (in opposition to NEW windows only). Because of this we had to suggest to the client to replace all windows in order to have about 1.4 in the all house (or the alternative would have been a passive house standard window 0.65 or so for the extension).

I'd get a new BER assessor. Did he have any expierence of construction before he entered the field? or is it just his nature.

It's easy to prove him wrong. Firstly;

Consider it like this, the lower the glazed area of the existing house, the more leeway you are entitled to with new windows. Which makes sense, right?

Does the above make sense to you? Can you see the basic reason for option a)


Secondly. Iftheir intention had of been to use the average for the whole house. Then that method is redundant as the extremely low U-values would never actually be used as going with option b) would be a much easier way of complying.

Using the whole house also leads to impossible situations were, for example a very large old house (protected structure) with plenty of existing original glazing, a modern addition would require glazing that is beyond current standards. Replacing all the glazing is not an option, so that (incorrect) view of part L prevents any addition or extension to many older houses.

Finally, option a and b are both equally acceptable, and therefore one would expect that they would have similar targets in most cases (granted some of the extreme cases may not). But taking a view that it is the whole house average will always leads to a big difference. Which alone would suggest that that view is wrong

icbarros

Thanks again Mellor!

Mellor wrote: »

I'd get a new BER assessor.

I'm definitely going to question him about this. That's one of the reasons I started the thread, I was not convinced that was the correct interpretation and I wanted to know other peoples opinion.

Mellor wrote: »

Using the whole house also leads to impossible situations were, for example a very large old house (protected structure) with plenty of existing original glazing, a modern addition would require glazing that is beyond current standards. Replacing all the glazing is not an option, so that (incorrect) view of part L prevents any addition or extension to many older houses.

It makes sense but Part L does not apply to works (including extensions) to an existing building which is a “protected structure”.

Mellor wrote: »

as going with option b) would be a much easier way of complying.

Mellor wrote: »

Finally, option a and b are both equally acceptable, and therefore one would expect that they would have similar targets in most cases (granted some of the extreme cases may not).

Interestingly this has not been the case in the last 2 extensions we did. It seems to me that the whole house method (a) is always more favourable (requires a not so low u-value).
And just for information I leave here the calculations:

Using all house method (a)
Af=90.62 sqm
Aope=36.81 sqm
Aope/Af=0.406
U=0.4325/0.406+0.27=1.33 W/m2K
Using extension alone method (b)
Af=17.36m2
Aope=20 sqm
Aope/Af=1.152
U=0.4325/1.152+0.27=0.64 W/m2K

But, as you said:

Mellor wrote: »

Building regulations apply to new works only.

And that makes sense to me!
Thanks again.

beyondpassive

One popular interpretation is that the Part L applies to areas where structure or fire regulations are brought into play (parts A+B regs). So if you put in a new steel beam to the old dining room, then the wall element that is affected must comply. So any windows in walls which have new structure applied must comply. If say there was a new bedroom on the 2nd floor, then the staircore would be a fire rated shaft, this would affect the whole house as this constitutes new works.

Its all very confusing

Mellor

icbarros, jsut seen the reply now and to close up an issue

icbarros wrote: »

It makes sense but Part L does not apply to works (including extensions) to an existing building which is a “protected structure”.

And extension to a protected structure would need to comply with part L.

Interestingly this has not been the case in the last 2 extensions we did. It seems to me that the whole house method (a) is always more favourable (requires a not so low u-value).
And just for information I leave here the calculations:

Using all house method (a)
Af=90.62 sqm
Aope=36.81 sqm
Aope/Af=0.406
U=0.4325/0.406+0.27=1.33 W/m2K
Using extension alone method (b)
Af=17.36m2
Aope=20 sqm
Aope/Af=1.152
U=0.4325/1.152+0.27=0.64 W/m2K

You misunderstood. The above is when both options are applied correctly. New windows under option a are required to be 1.33 W/m2K.

My point was to disprove the idea that option a is the average of all windows (including existing). As the existing windows are likely to be way above 1.33 W/m2K, the new windows are would have to be way below.


Also is your example right, taking the extension only figures away from the whole figures leaves 73m.sq floor area with 16.8m.sq opes, appears a bit low. (extension appears to be highly glazed which accounts for the very low figure in method b)

icbarros

Mellor wrote: »

Also is your example right, taking the extension only figures away from the whole figures leaves 73m.sq floor area with 16.8m.sq opes, appears a bit low. (extension appears to be highly glazed which accounts for the very low figure in method b)

Yes, I double checked the figures and they are correct.
Extension is indeed highly glazed, but not fully glazed.
It's not the 1st time that we have an extension that comes with a VERY low u-value if using method (b)...
Following some quick calculations (and 'reverse' calculations using Formula on Table 6) I am inclined to think that method (b) is not worth to use for any extension that has an area of opes equivalent to 40% of the floor area (or more). And that's to achieve an u-value of approx. 1.4, which is pretty standard these days.

sinnerboy

Sorry to be late in here but I interpret differently -

Method A applies when all windows are being replaced , Method B when they are not.

Whichever is better will vary from case to case.

Lets start with a fixed parameter of Uw - 2.0 for new windows.

We may or may not replace the existing

Example .

Existing house Afx = 100m2
Existing windows Awx = 25m2

Extension Afp 50m2
Proposed windows Awp = 20m2

Method a)

Afx+Afp = 150m2
Awx + Awp = 45m2

45*100 /150 = 30%

From Table 5

Uw must be </=1.7 or
Awx + Awp must be </= 25% of Afx+Afp = 37.5m2 meaning we can only have 12.5 m2 in our extension.

Either we reduce the area of glazing or improve its U Value to 1.7

Method b)

Awp/Afp = 20/50 = 40%

From Table 5 Uw must be 1.3 </= ( quick interpolation ) or
Awp must be </= 25% of Afp = 12.5m2 plus area of existing windows "covered over" by the extension.

Lets suppose for simplicity of example we are covering over 7.5m2 of existing window.

We can have our 20m2 . But we must buy windows at 1.3 U value.

sinnerboy

Mellor wrote: »

And extension to a protected structure would need to comply with part L.

No - from 0.5.1 APPLICATION TO BUILDINGS OF ARCHITECTURAL OR HISTORICAL INTEREST TGDL 08 ( it's in Draft 2010 too )

Part L does not apply to works (including extensions) to an existing building which is a “protected structure” or a ‘proposed protected structure” within the meaning of the Planning and Development Act 2000 (No 30 of 2000). Nevertheless, the application of this Part may pose particular difficulties for habitable buildings which, although not protected structures or proposed protected structures, may be of architectural or historical interest. Works such as the replacement of doors, windows and rooflights, the provision of insulated dry lining and damp-proofing to walls and basements, insulation to the underside of slating and provision of roof vents and ducting of pipework could all affect the character of the structure.
In general, the type of works described above should be carefully assessed for their material and visual impact on the structure. Historic windows and doors should be repaired rather than replaced

The Conservation lobby is very strong in Ireland. I'd face the combined All Black scrum pack first.

Mellor

icbarros wrote: »

Yes, I double checked the figures and they are correct.

Are you removing any windows or building over them.?

Following some quick calculations (and 'reverse' calculations using Formula on Table 6) I am inclined to think that method (b) is not worth to use for any extension that has an area of opes equivalent to 40% of the floor area (or more). And that's to achieve an u-value of approx. 1.4, which is pretty standard these days.

You are looking at this the wrong way. 40% more is a huge % of glazing, and is very very inefficient. I would be off the opinion that designing for glazed areas above 40% is bad, not method b.

However, I wouldn't consider it a hard and fast rule, some small extensions, such as sun rooms, will have % near 100%, so for small extension, the above comments don't apply.

sinnerboy wrote: »

Method A applies when all windows are being replaced , Method B when they are not.

I respectively disagree SB.
Obviously, I'm personally not using part L remotely as often as others, but I have read the relevant sections a few times before have never seen mention that A applies only where you change all windows, or that you must average the windows for the whole house.

My reasoning for it not to be included has been given above.
Building regs cannot force retrospective work, plus the other reasons stated.

Furthermore, changing the windows in the existing dwelling is a material change, and is under a separate column is table 5. And as set out in section 2.1.2.6, it is imposed the limitation of 2.0

2.1.2.6 This Part of the Building Regulations applies
to the replacement of external doors, windows, or
rooflights in an existing dwelling. The average Uvalue
of replacement units should not exceed the
value of 2.0 W/m2K set out in Table 5.

Example .

Existing house Afx = 100m2
Existing windows Awx = 25m2

Extension Afp 50m2
Proposed windows Awp = 20m2

Method a)

Afx+Afp = 150m2
Awx + Awp = 45m2

45*100 /150 = 30%

From Table 6

Uw must be </=1.7 or
Awx + Awp must be </= 25% of Afx+Afp = 37.5m2 meaning we can only have 12.5 m2 in our extension.

Either we reduce the area of glazing or improve its U Value to 1.7

Nobody disputes how to do the calculations. (I edited a small part, its table 6 not five, just so others don't get confused)

The above doesn't address the issue of if 1.7 applies to new windows, or to new and existing.

Method b)

Awp/Afp = 20/50 = 40%

From Table 6 Uw must be 1.3 </= ( quick interpolation ) or
Awp must be </= 25% of Afp = 12.5m2 plus area of existing windows "covered over" by the extension.

Lets suppose for simplicity of example we are covering over 7.5m2 of existing window.

We can have our 20m2 . But we must buy windows at 1.3 U value.

This last line is wrong, prob a typo. (it would of been right had you not mentioned covering over 7.5m2)

U-value 1.3 allows us top have 40% (20m2) + 7.5m2 = 27.5m2
U-value 2.0 allows us top have 25% (12.5m2) + 7.5m2 = 20m2

sinnerboy wrote: »

No - from 0.5.1 APPLICATION TO BUILDINGS OF ARCHITECTURAL OR HISTORICAL INTEREST TGDL 08 ( it's in Draft 2010 too )

Part L does not apply to works (including extensions) to an existing building which is a “protected structure” or a ‘proposed protected structure” within the meaning of the Planning and Development Act 2000 (No 30 of 2000). Nevertheless, the application of this Part may pose particular difficulties for habitable buildings which, although not protected structures or proposed protected structures, may be of architectural or historical interest. Works such as the replacement of doors, windows and rooflights, the provision of insulated dry lining and damp-proofing to walls and basements, insulation to the underside of slating and provision of roof vents and ducting of pipework could all affect the character of the structure.
In general, the type of works described above should be carefully assessed for their material and visual impact on the structure. Historic windows and doors should be repaired rather than replaced

The Conservation lobby is very strong in Ireland. I'd face the combined All Black scrum pack first.

I think you may be misunderstanding me here.
I don't disagree with any of the terms you bolded. I never said part L applies to them. It should be obvious that it doesn't. Period architecture remains as period architecture.

However, extensions are a different matter. Should the extension attempt to integrate itself into the original (a design strategy I don't agree with, but a different issue) then no part L doesn't apply and period details can be used.

But, if the extension is a modern styled structure, structurely separate and linked to the orginal. Then, imo, part L should be applied as there is no good reason not to. In order to justify this application of part L, i'd reference the fact the TGD is guidence, not law, and the situation described in 0.5.1 was not intended for modern styled structures.

An example of this would be an old manor house, that by means of a large extension was converted to a hotel. The modern part should have to meet part L imo, regardless of beign technically an extension. (before somebody points out the obvious - Parl L BotD also contains the same exclusion for protected structures)

icbarros

Mellor wrote: »

Are you removing any windows or building over them.?

We are building over one window and one door. And keeping the existing windows as they are.

Mellor wrote: »

You are looking at this the wrong way. 40% more is a huge % of glazing, and is very very inefficient. I would be off the opinion that designing for glazed areas above 40% is bad, not method b.

However, I wouldn't consider it a hard and fast rule, some small extensions, such as sun rooms, will have % near 100%, so for small extension, the above comments don't apply.

I understand your point although the efficiency can be optimized by using good specifications for all elements.
Often small extensions are done for houses with bad layouts where the natural light and sun path were disregarded by the original designer. Their occupants are eager to get the maximum from the sun hence the desire for a highly glazed extension.

Mellor wrote: »

have never seen mention that A applies only where you change all windows

I have to agree with Mellor here.

Mellor wrote: »

Furthermore, changing the windows in the existing dwelling is a material change, and is under a separate column is table 5. And as set out in section 2.1.2.6, it is imposed the limitation of 2.0

Material changes/alterations could be a different thread all together but since it's also related with interpretation of Part L I'll explore this a bit.

A material alteration is an alteration which affects any part of the structure or fire safety of the building.
And from the 'Planning Act':

"alteration’’ includes—
(a) plastering or painting or the removal of plaster or stucco, or

(b) the replacement of a door, window or roof,that materially alters the external appearance of a structure so as to render the appearance inconsistent with the character of the structure or neighbouring structures

Following this I have to disagree with Mellor and "changing the windows in the existing dwelling" is not a material alteration. Unless the new windows would "render the appearance inconsistent with the character of the structure or neighbouring structures".

Mellor wrote: »

The above doesn't address the issue of if 1.7 applies to new windows, or to new and existing.

Good point. And that's really the main issue here.

Mellor

icbarros wrote: »

Material changes/alterations could be a different thread all together but since it's also related with interpretation of Part L I'll explore this a bit.

A material alteration is an alteration which affects any part of the structure or fire safety of the building.
And from the 'Planning Act':

Firstly, definitions in the planning act have no direct relationship to the TGDs or building regs.
The above quote text relates to where a alertation requires planning permission.

If you are replacing new windows, they have to comply. The text I quoted above states the min requirements.

also, Part L states;

0.1.7 This amendment applies to all works to
existing dwellings that are covered by the
requirements of the Building Regulations, including
extensions, material alterations, material changes of
use and window and door replacement.

Mellor wrote:

The above doesn't address the issue of if 1.7 applies to new windows, or to new and existing.

Just to reinforce my opinion that it applies to new work only.

Part L wrote:

Table 5
Note 2: For material alterations, the U-values relate to the new
works

I'm not saying that this directly relates to extensions, it doesn't. But it provides insight to the intentions of the regs relating to existing structures, regarding practicality.

I think this thread has highlighted a flaw of the current part L. There should be no doubt. There should be a note included with either option A that states the appliaction