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External Insulation question



  • Registered Users Posts: 2,041 ✭✭✭gooner99

    Thanks. Sounds like we would be best to remove the existing broken footpaths in to the existing walls to allow the installer to more easily go lower with the external Insulation. My understanding is that a different type of material is used below dpc?

  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    Yes, remove all footpaths that you need / wish to be replaced, and fit the XPS insulation down as low as is possible below the floor level.

    The material used below ground level should specifically be certified for that purpose.

    All materials have Certification. Request and read copies for all materials, before any works commence.

    The below DPC and below ground insulation must be a ‘closed cell’ or ‘single mono cell’ construction. This means that all the tiny minute cells in the material are not connected to the adjoining cells. The material is impervious. (opposite to porous).

    One other very important issue - make the EWI contractors cover all your existing window frames and All panes of glazing before commencement. The Contractor should do this with Glass and Window Protection Self-Adhesive Film:-

    This should be used on all windows and external doors on ALL building sites.

    If this protection is not used the Glazing will be scratched and the contractor will state that the scratches were there before they commenced.

    Scratched glazing cannot be repaired and will need to be replaced.

  • Registered Users Posts: 116 ✭✭CandyButcher

    Hello Mr Eastwood,

    I have read your eye opening comments here and want to say thank you for pointing these infuriating points out to the people. Including myself.

    Tell me, is there any potential devastating risks with internal plasterboard insulation?, or shall I stick to throwing logs on the stove..

    Buying a E rated home could you give me any safe insulation methods that will bypss the “experts” potentially destroying my life. How Boyt attic insulation and internal walls would that be a safe bet ?

  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    Thanks for your comments

    I always recommend Internal insulation

    300 mm of fibreglass insulation resting on the ceiling slabs is perfect.

    Ensure every hole/ gap in the ceiling is filled:-

    1. Holes around pipes passing through the ceiling of the hot press
    2. Make the attic access door airtight
    3. Holes around where the wires pass through the ceiling to pendant lights

    The walls should be dry with no rising dampness

    Fix approximately 70 mm slab with insulation (or thicker if you wish).

    Fit insulated slabs to the internal reveals and Soffit of doors and windows opes, - whatever max thickness will fit.

    If there are concrete block internal walls (perpendicular to external walls) and built in to the external walls, fit slabs with at least 25 mm insulation on these internal walls.

    If other internal walls plaster is not perfect- then fix 12 mm slabs on these walls.

    You can do 1 room at a time to suit budget and accommodation needs.

    Double glazing is also important.

    Burning logs is fine, with well insulated walls and ceilings- the rooms will stay warmer for longer periods of time, because there will be less heat loss.

  • Registered Users Posts: 116 ✭✭CandyButcher

    Thank you so much for taking the time for the informative reply mate. The walls are cavity block so ill request throwing up 25mm on them each side of the house.

    Thanks again!

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  • Registered Users Posts: 27 tomahawke

    Extremely informative thread. C. Eastwood thanks so much for the detailed insights and recommendations. There are some many opinions on this subject online some of which completely contradict others so the decision-making process for a lay person is a nightmare. I am about to embark on my own insulation project at home and I thought I had it all sussed until I read this thread. I would value your view on the my own plan. Here's the setup and the plan in a nutshell:


    • Detached house built late 1990s
    • Coastal but not exposed
    • Two sides cavity walls. Front wall and one side wall (yellow brick on the outside of both). I suspect zero or very little insulation in these. They are drylined with basic fibreglass insulation on the inside
    • Two sides cavity block.


    • Cavity Walls:
      • *Fill cavity walls with bonded beads per SEAI recommendation.
      • Externally insulate. I understand that I may need to reinstate the yellow brick with brick slips on the external insulation and I know that will be costly. I'm hoping I can get away with doing this just on the front wall. Need to discuss with Planning.
    • Cavity Block Walls:
      • Externally insulate
      • Since these walls cannot be pumped, cap off at the top to mitigate convection.


    • TBD but plan would be to enhance internal ventilation (possibly with mini, fan assisted, heat exchange vents in selected rooms downstairs. These types of vents would not be suitable for bedrooms in my opinion due to the sound of the fan. I already have aereco mechanical vents in the bedrooms which work with fans in the bathroom and ensuite so I think I'm ok upstairs - little or no condensation on windows even on the coldest of days.

    All windows are triple glazed and the attic is well insulated.

    What do you think? Whilst not completely ruled out, an internal approach would be very disruptive and my main concern there is that you would have gaps at the floor/ceiling level as opposed to the full wrap-around of the external wall insulation.

    *From your quoted comments the beads would prevent/mitigate convection but would they prevent any potential rising damp? There is no damp in the walls at the moment but the area of the house near the side cavity wall is particularly cold so I suspect zero or very little insulation there.

    No worries if you can't get to this. The thread alone has been very very informative.

    Many Thanks

  • Registered Users Posts: 166 ✭✭Dr.Tom

    Some window companies offer an extension piece either end of their window frame to allow reveal insulation to butt up to it and tie in thus preventing the cold bridge.

  • Registered Users Posts: 1,059 ✭✭✭TimHorton

    Thermal Mass ? Where is it when you insulate all walls internally and 300 mm in ceiling.