Repairing large cavity above wooden window - advice needed please.

[PianoJames]

Hello everyone, I'm new to the forum and hoping to find some advice. I've started restoring a grade 2 listed 15th century cottage. The windows are generally in bad shape but repairable but I am stumped as to what to do above this first floor window. The render flairs out above and underneath has been previously filled in with timber which has now rotten - see picture, both the white and black with holes are completely shot but the black frame behind seems ok(ish).

I am reluctant to dig out the rotten timber until I have a solution as it will leave a sizeable cavity under the render flair. Any suggestions on how to proceed? I have thought about replacing with timber, but cannot see how I would fix it as the frame does not extend up enough to attach. Mortar seems extremely tricky too. Any thoughts much appreciated!

 

[Cubist]

Please confirm this is a timber frame cottage/house. In such structures it is not unusual to find the window and door frames are set with a gap above the header and side rails with the purpose of avoiding damage resulting from the annual movement cycles affecting the buildings frame. Typically these gaps are bridged using blocks of wood to all the window/door frames to be tied to the building and the gap then closed with a suitable wooden moulding that would then be caulked to prevent rainwater penetration.

My worry at the present is that the top most frame element you are describing/referring to is in fact a bridging lintel or a bressummer beam.

 

[PianoJames]

Please confirm this is a timber frame cottage/house. In such structures it is not unusual to find the window and door frames are set with a gap above the header and side rails with the purpose of avoiding damage resulting from the annual movement cycles affecting the buildings frame. Typically these gaps are bridged using blocks of wood to all the window/door frames to be tied to the building and the gap then closed with a suitable wooden moulding that would then be caulked to prevent rainwater penetration.

My worry at the present is that the top most frame element you are describing/referring to is in fact a bridging lintel or a bressummer beam.

Many thanks for your reply. Yes it is a timber framed building, rendered externally so the beams are not visible from outside. From what I can see this is not a lintel but a rotten wood infill.

 

[Cubist]

If you are confident the beam immediately above and spanning that window frame is in good condition and the rot is limited to the timber used to close gap then a suitable repair using a replacement fillet should be possible. The key issues though would surround;

• How the old fillet was/is fixed in place to the house frame and window frame respectively?
• Whether the wooden bocks used for that purpose are still in a good condition?
• Access to permit insertion and fixing of new blocks if needed?
• The means to shape and tailor a new fillet to close the gap?
• Potential for damage/loss of some of the render forcing a need for repair.

Could you save a photo of the, ideally exposed, beam spanning that window and the frame header please? That may offer some additional clues.

 

[PianoJames]

If you are confident the beam immediately above and spanning that window frame is in good condition and the rot is limited to the timber used to close gap then a suitable repair using a replacement fillet should be possible. The key issues though would surround;

• How the old fillet was/is fixed in place to the house frame and window frame respectively?
• Whether the wooden bocks used for that purpose are still in a good condition?
• Access to permit insertion and fixing of new blocks if needed?
• The means to shape and tailor a new fillet to close the gap?
• Potential for damage/loss of some of the render forcing a need for repair.

Could you save a photo of the, ideally exposed, beam spanning that window and the frame header please? That may offer some additional clues.

The attached photos show the beam from the inside - it is not visible from the outside. The frame header is the black section in the middle of the second photo. It is reasonably sound but certainly not perfect. I can feel through the hole I've made that the top of the frame header is slightly soft on top and I can feel a void where the infill has rotted. I can also feel the beam behind which is slightly soft but (I hope) salvageable as there are no signs so far of problems inside and it is a substantial timber.

My concern about replacing the timber infill is how to attach it if the frame header is too badly damaged. I would obviously like to avoid replacing the entire window. The render flair is supported by a metal trim, as you use in plastering but not visible here.

 

[Cubist]

Just to confirm my understanding and using this last photo for direct reference;

• The white painted section to the left is part of the header rail.
• The first black painted section is also part of the header rail.
• The rightmost black section is the fillet closing the gap between the rail and the render.

Can you confirm also that a very thin blade can be run behind and along the render line and the fillet with/without encountering an obstruction? Also, that the header rail and the fillet are more or less horizontal?

Sorry for these extra questions but this latest photo has me puzzling.

 

[PianoJames]

Just to confirm my understanding and using this last photo for direct reference;

• The white painted section to the left is part of the header rail.
• The first black painted section is also part of the header rail.
• The rightmost black section is the fillet closing the gap between the rail and the render.

Can you confirm also that a very thin blade can be run behind and along the render line and the fillet with/without encountering an obstruction? Also, that the header rail and the fillet are more or less horizontal?

Sorry for these extra questions but this latest photo has me puzzling.

Yes you are correct. The white section on the left is what the windows close against (I've taken them off to restore them more easily). The left black section is the header - looks like 2×4 type timber. The right most black section is infill along with the right most white section (it's been painted two different colours) and looks like one of those weather strips you get on the bottom of doors with a triangular profile. I can confirm that the infill is not connected to the render as far as I can see but most of it is still painted over. I can't tell how the infill is currently fixed to the header.

 

[PianoJames]

Yes you are correct. The white section on the left is what the windows close against (I've taken them off to restore them more easily). The left black section is the header - looks like 2×4 type timber. The right most black section is infill along with the right most white section (it's been painted two different colours) and looks like one of those weather strips you get on the bottom of doors with a triangular profile. I can confirm that the infill is not connected to the render as far as I can see but most of it is still painted over. I can't tell how the infill is currently fixed to the header.

My current thinking is to build out above the good wood of the header and then up to the render from there (see attached cross section). My question then is then could the void this creates be filled with mortar so as to further protect the structural beam behind or is it best left as a void? My instincts tell me to fill it with something that can breathe, such as lime mortar.

 

[Cubist]

Sorry for the tardy reply but despite the opportunity to consider I can see no alternative but to remove the rotten material to determine the full extent of the challenge and then formulate a plan of action. Everything depends on how much of that header is in good condition and how much free room there may then be after its removal to allow the insertion of new wooden supports above the header and behind the render line. Your plan above is a fair starting point I think but it will obviously need to be adapted as the detail is revealed.