Accuracy of dimensions of planning drawings.

Accuracy of dimensions of planning drawings.

Postby john242 » Wed Mar 21, 2012 12:30 am

Can any let me know on what the required accuracy of the as built structure dimensions of a building must be in order to be considered compliant.

I have a project which is about to start on site with planning permission. The planning drawing have full dimensions both overall for the external footprint and internally within rooms.

The client has requested that the external cavity wall be increase from a standard 300mm as shown on planning drawings to a 465 mm wall but to maintain the internal room dimensions. This effectively increase the footprint of the building by 165mm on all sides.
Is this still considered compliant with the granted permission.
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Re: Accuracy of dimensions of planning drawings.

Postby pico » Wed Mar 21, 2012 3:12 pm

Strictly should be exact to be compliant, and client should be advised of this.

However you / they could consider the liklihood of enforcement proceedings if you did build the extra 165mm each side, and make a call.

It would be worth drawing the new footprint on a site plan and each level and seeing if there is any significant impact on adjacent boundaries, at all levels, particularly if you are close to any particular boundary.
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Re: Accuracy of dimensions of planning drawings.

Postby JohnArch » Wed Mar 21, 2012 3:42 pm

The scale of the change would in view be a contravention of the planning permission. You should advise your client accordingly and that they run the risk of enforcement proceedings and ending up with a structure that does comply with the grant of permission.
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Re: Accuracy of dimensions of planning drawings.

Postby shadow » Wed Mar 21, 2012 10:17 pm

Before making any decision in this regard some real advice should be sought. If the increase of the building is in terms of footprint but without an increase in the internal area it "may" be considered appropriate. This especially occurs in the lifetime of a planning permission where changes in performance criteria forces construction changes which are outside the control of architect or planner or client. This varies according to the requirements some are dated to the planning others do the date of construction. Ideally the extent of the building should always be within the volume, height, shape, form of the material in the application. This would mean that the client takes the hit on the project with reduced areas. If the interior is planned to the millimetre this may be detrimental to the plan such as in kitchen planning. It should be noted that planning is a principle based licence and not a licence to ignore property rights, or other legal restraints. Moreover it is not the building control act which governs the actual building standards. A simple procedure would be get a ruling from the planning authority regarding the interpretation. A meeting to discuss the situation prior to making a more formal submission would be in order. However we have found that most local authorities have taken an overly legal position on these issues forcing people to go into planning especially where there is any greyness. It is certainly very expensive if it all goes wrong. This is one of the main problems with the split between planning and building control and the lack of determination. In the UK where planning and building control issues are considered simultaneously this does not arise and moreover because of site inspections by local authority surveyors variation is not undertaken without consultation or compliance being sought.
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Re: Accuracy of dimensions of planning drawings.

Postby henno » Thu Mar 29, 2012 11:51 am

there is a phrase that an bord pleanala use often to describe very small discrepancies between what was applied for and what was built.... its called "de minimus" which basically means insignificant.

in your case context is key... does the extra wall construction width 'significantly' impact separation distances to boundaries , or 'signigicantly' impact the mass of the elevations??

most probably not... and the argument can be made that both:
1. the initial wall construction width wouldnt allow for building regulation compliance
2. the extra width is required to achieved above minim reg compliance.


so if you are the certifier its up to you to make a judgement on this.
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Re: Accuracy of dimensions of planning drawings.

Postby onq » Mon May 14, 2012 3:26 pm

John 242,

You are not getting paid to carry risk introduced at a late stage, however well-intentioned.


  • The building is now wider by 350mm on all elevations.
  • The front and possibly the rear elevations are probably out of alignment with the adjoining property, assuming they lined up on the permission.
  • All of the elevational details will change, especially the opes and particularly the cills, eaves, locations of gullies, downpipes etc.
  • If you have already done a Bill of Quantities, there will be additional lengths for every pipe penetration.
  • The side passage may now be impassable, since 165mm is not a minor amount by which to diminish a narrow passageway.
  • If the distance to the boundary from windows is less than 1.0M there may be a fire implication and there may be implications for the later installation, opening up or variation of opes or glazing which could be dealt with under the exempted development regulations.

IMO you should seek a Section 5 Declaration (€80 and four weeks, last time I checked) that the change constitutes exempted development.

Just to underline the seriousness of how the local authority is taking this in relation to upgrading existing buildings, Dun Laoghaire-Rathdown Co Co now require drawings showing the proposed changes and will not give a response over the phone.

I expect a recent grant will attract the same diligence.

ALTERNATIVELY...

You're a designer, so design your way out of the problem.
You could possibly source an insulation with a higher thermal resistance than that proposed, this allowing a greater retention of heat for lesser depth of insulation.

BTW if your wall is blockwork (100mm block/ 100mm cavity/ 100mm block) and you're upping the size of the structural cavity from 100mm you need to be totally clear on what you're doing. Above 100mm I always ask for an engineers comments.

You may be advised to use a different form of construction.

Before you commit to anything either before a BER check on the cost/benefits. Insulation is often the best way to go, but the structure and detailing must be balanced. There is no point increasing the cavity and then not properly sealing the insulation to the inner leaf. There is equally no point in building in two 100mm leaves with infill insulation when a 215mm solid leaf with external weathering and insulation might over a significant cost reduction for the same level of insulation.

As always, with this depth of insulation you really need to nail your transition/junction details and do a pressure test.

And don't forget your renewables. No point doing all this insulating and still using electricity to heat the place!

Best of luck with it and you might let us know how you get on.
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Re: Accuracy of dimensions of planning drawings.

Postby onq » Mon May 14, 2012 5:55 pm

Plus a colleague reminded me this afternoon that this will significantly affect the separation distance between new houses - some LA's require a MINIMUM of 2.3M - Check it out.
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