In short
Replacing a roof like for like, in the same material and colour, is normally permitted development in Wales and needs no planning application. It can need consent when the material or colour changes on a visible slope inside a conservation area, on a listed building (where listed building consent is needed for almost any change), or inside Bannau Brycheiniog (Brecon Beacons) or Eryri (Snowdonia) national parks, where the park authority is the planning authority and expects natural slate. Building Regulations apply separately to any roof re-covered over half its area.
This is a job for our Roof replacement service.
Like for like
Slate off, slate on, same colour, same profile: permitted development, no application. Most re-roofs in Powys and Ceredigion are this.
Where it changes
Conservation areas
Newtown, Welshpool, Llanidloes, Llandrindod Wells, Brecon, Hay-on-Wye, Presteigne, Montgomery, Aberystwyth, Aberaeron, Cardigan, New Quay and Lampeter all have conservation areas covering their historic centres. Inside them a change from slate to tile, or to a different colour, on a slope that can be seen from a public place is where Powys or Ceredigion County Council may require an application. Ask the council's conservation officer before quoting; they answer quickly and it is free.
Listed buildings
Listed building consent is needed for almost any work that affects the character of a listed building, and the roof is character. Even like-for-like re-slating can need consent if the coursing or the ridge detail changes. Presteigne, Montgomery and Aberaeron have a high proportion of listed houses.
The national parks
Brecon, Crickhowell and the villages around them are inside Bannau Brycheiniog National Park; the countryside around Machynlleth runs into Eryri. The park authority, not the county council, is the planning authority there, and both expect natural slate on visible roofs and take an interest in rooflights, solar panels and dormers.
Building Regulations, separately
Re-covering more than half of a roof is notifiable under the Building Regulations in Wales whatever the planning position. Installers registered with a competent person scheme self-certify; otherwise the work is notified to the council's building control. A roof over a heated room may also need to meet the current insulation standard.
Who to ask
The roofer we pass your enquiry to should raise all of this before quoting. For the definitive answer: Powys County Council or Ceredigion County Council planning, or the national park authority for a property inside one.